refactor(rustfs): split object_usecase.rs into per-operation app/object modules (#6670)

* refactor(rustfs): carve app/object out of object_usecase.rs — shared, extract, test_support children (backlog#1841 step 1)

Mechanical move-only split of rustfs/src/app/object_usecase.rs (19.7K lines). The file body moves to rustfs/src/app/object/mod.rs, and the first self-contained slices move into children: shared.rs (cross-cutting helpers: quota admission, response checksum injection, object-lock write validation, table-catalog mutation guard, deadlock request guard, proxy passthrough utilities), extract.rs (snowball auto-extract path incl. tar/pax helpers and execute_put_object_extract), and cfg(test) test_support.rs for cross-module test scaffolding. object_usecase.rs stays as a thin pub use facade so every existing crate::app::object_usecase:: path keeps working.

No behavior change: items move verbatim; the only source edits are visibility widenings required by the new module boundaries (private -> pub(super); pub(super) -> pub(crate) for the three helpers multipart_usecase and the app gating tests import). Guard scripts that pinned rustfs/src/app/object_usecase.rs now scan the rustfs/src/app/object tree, and the table_catalog source-text guard test concatenates the split files.

* refactor(rustfs): move the GetObject read path into app/object/get.rs (backlog#1841 step 2)

Move-only continuation of the object_usecase split: cold-fill orchestration, disk-permit admission, streaming readers and resume control, stream-buffer tuning, execute_get_object / execute_get_object_attributes, the GET replication proxy helpers, and their unit tests move from app/object/mod.rs into app/object/get.rs. Items keep their original text; cross-module call sites rely on the visibility widenings introduced in step 1.

* refactor(rustfs): move the PutObject and CopyObject paths into app/object (backlog#1841 step 3)

Move-only continuation: put.rs takes the PUT body admission and timeout readers, zero-copy and eager-commit machinery, execute_put_object, and the PUT unit tests; copy.rs takes the copy namespace/lifecycle lock helpers and execute_copy_object with its tests. Two source edits beyond visibility widenings: PutObjectChecksums fields become pub(super) (read by shared::apply_trailing_checksums across the new module boundary) and one relative super::storage_api call in the copy path becomes crate::app::storage_api since super now resolves to app::object. The table_catalog source-text guard concatenates the new files.

* refactor(rustfs): finish the object_usecase split — delete, head, restore modules (backlog#1841 step 4)

Move-only completion: delete.rs takes the delete helpers, cfg(test) delete hooks, and execute_delete_object/execute_delete_objects; head.rs takes execute_head_object with the HEAD replication proxy helpers; restore.rs takes execute_restore_object. app/object/mod.rs is now just the shared import prelude, module wiring, and the DefaultObjectUsecase struct with its constructors, accessors, and the execute_select_object_content delegation; the emptied tests module is gone. The delete re-export glob is cfg(test)-gated because its only cross-module consumers are the delete test hooks.

The table_catalog source-text guard now isolates the delete entrypoints from app/object/delete.rs, and doc/comment references that pointed at rustfs/src/app/object_usecase.rs internals now point at the per-operation modules.

scripts/check_architecture_migration_rules.sh

@@ -2166,7 +2166,7 @@ fi
 
 (
   cd "$ROOT_DIR"
-  rg -n --with-filename 'crate::app::(?:bucket_usecase|multipart_usecase|object_usecase)|Default(?:Bucket|Multipart|Object)Usecase::from_global\(\)' \
+  rg -n --with-filename 'crate::app::(?:bucket_usecase|multipart_usecase|object_usecase|object\b)|Default(?:Bucket|Multipart|Object)Usecase::from_global\(\)' \
     rustfs/src/storage/ecfs.rs \
     --glob '*.rs' || true
 ) >"$RUSTFS_STORAGE_ECFS_USECASE_BYPASS_HITS_FILE"
@@ -2220,7 +2220,7 @@ fi
 
 (
   cd "$ROOT_DIR"
-  rg -n --with-filename 'use crate::storage::\*;' rustfs/src/app --glob '*_usecase.rs' || true
+  rg -n --with-filename 'use crate::storage::\*;' rustfs/src/app --glob '*_usecase.rs' --glob 'object/*.rs' || true
 ) >"$RUSTFS_APP_USECASE_STORAGE_WILDCARD_HITS_FILE"
 
 if [[ -s "$RUSTFS_APP_USECASE_STORAGE_WILDCARD_HITS_FILE" ]]; then
@@ -2238,7 +2238,7 @@ fi
 
 (
   cd "$ROOT_DIR"
-  rg -n --with-filename 'crate::storage::s3_api::|use crate::storage::s3_api|super::s3_api::|use super::s3_api' rustfs/src/app --glob '*_usecase.rs' || true
+  rg -n --with-filename 'crate::storage::s3_api::|use crate::storage::s3_api|super::s3_api::|use super::s3_api' rustfs/src/app --glob '*_usecase.rs' --glob 'object/*.rs' || true
 ) >"$RUSTFS_APP_USECASE_S3_API_BYPASS_HITS_FILE"
 
 if [[ -s "$RUSTFS_APP_USECASE_S3_API_BYPASS_HITS_FILE" ]]; then
@@ -2250,13 +2250,13 @@ fi
   {
     rg -n --with-filename \
       '(use crate::storage::(access|helper|options|request_context|sse|timeout_wrapper|head_prefix|concurrency|ecfs)|crate::storage::sse::EncryptionKeyKind|use crate::storage::\{|use crate::storage::[A-Z])' \
-      rustfs/src/app/select_object.rs rustfs/src/app/*_usecase.rs || true
+      rustfs/src/app/select_object.rs rustfs/src/app/*_usecase.rs rustfs/src/app/object || true
     rg -n --with-filename \
       'use super::(?:\{[^}]*\b(?:DynReader|HashReader|WriteEncryption|WritePlan|DecryptReader|EncryptReader|HardLimitReader|boxed_reader|wrap_reader|compression_metadata_value|is_disk_compressible|MIN_DISK_COMPRESSIBLE_SIZE|get_lock_acquire_timeout|is_valid_storage_class|StorageError|DiskError|is_all_buckets_not_found|is_err_bucket_not_found|is_err_object_not_found|is_err_version_not_found)\b|(?:object_api_utils::to_s3s_etag|storageclass|StorageError|DiskError|DynReader|HashReader|WriteEncryption|WritePlan|DecryptReader|EncryptReader|HardLimitReader|boxed_reader|wrap_reader|compression_metadata_value|is_disk_compressible|MIN_DISK_COMPRESSIBLE_SIZE|get_lock_acquire_timeout|is_valid_storage_class|is_all_buckets_not_found|is_err_bucket_not_found|is_err_object_not_found|is_err_version_not_found)\b)' \
-      rustfs/src/app/bucket_usecase.rs rustfs/src/app/object_usecase.rs rustfs/src/app/multipart_usecase.rs rustfs/src/app/lifecycle_transition_api_test.rs || true
+      rustfs/src/app/bucket_usecase.rs rustfs/src/app/object_usecase.rs rustfs/src/app/object rustfs/src/app/multipart_usecase.rs rustfs/src/app/lifecycle_transition_api_test.rs || true
     rg -n --with-filename \
       'use super::(?:\{[^}]*\b(?:AppObjectLockConfigExt|AppReplicationConfigExt|AppVersioningConfigExt|predict_lifecycle_expiration|validate_restore_request|bucket_target_sys|lifecycle|metadata|metadata_sys|object_lock|policy_sys|quota|replication|tagging|target|utils|versioning_sys|transition_api|ObjectInfo|ObjectOptions)\b|(?:AppObjectLockConfigExt|AppReplicationConfigExt|AppVersioningConfigExt|predict_lifecycle_expiration|validate_restore_request|bucket_target_sys|lifecycle|metadata|metadata_sys|object_lock|policy_sys|quota|replication|tagging|target|utils|versioning_sys|transition_api|ObjectInfo|ObjectOptions)\b)|super::(?:lifecycle|metadata_sys|object_lock|quota|replication|tagging|target|utils|versioning_sys|transition_api)::|super::super::(?:metadata_sys|lifecycle|target)::' \
-      rustfs/src/app/bucket_usecase.rs rustfs/src/app/object_usecase.rs rustfs/src/app/multipart_usecase.rs rustfs/src/app/lifecycle_transition_api_test.rs rustfs/src/app/capacity_dirty_scope_test.rs rustfs/src/app/context.rs rustfs/src/app/context/handles.rs rustfs/src/app/context/interfaces.rs rustfs/src/app/context/runtime_sources.rs || true
+      rustfs/src/app/bucket_usecase.rs rustfs/src/app/object_usecase.rs rustfs/src/app/object rustfs/src/app/multipart_usecase.rs rustfs/src/app/lifecycle_transition_api_test.rs rustfs/src/app/capacity_dirty_scope_test.rs rustfs/src/app/context.rs rustfs/src/app/context/handles.rs rustfs/src/app/context/interfaces.rs rustfs/src/app/context/runtime_sources.rs || true
   }
 ) >"$RUSTFS_APP_USECASE_STORAGE_API_BYPASS_HITS_FILE"