refactor(ecstore): drop the client shim, import rustfs-s3-client directly (#6668)

* refactor(ecstore): drop the client shim, import rustfs-s3-client directly

Completes the migration window opened by the rustfs-s3-client extraction (rustfs/backlog#1842 PR3): every consumer now imports the client crate directly and the crate::client shim is deleted.

- All in-crate crate::client:: paths (tier warm backends, tier core, lifecycle tier_sweeper, replication storage boundary, set_disk) now import rustfs_s3_client::* directly; crates/ecstore/src/client/mod.rs and the lib.rs mod client declaration are gone.
- The two server-side modules historically misfiled under client/ move to their real homes: object_api_utils.rs to crates/ecstore/src/object_api/ (it builds engine-side object readers/writers), and object_handlers_common.rs to crates/ecstore/src/bucket/lifecycle/ (it is the lifecycle noncurrent-version cleanup helper). The latter now routes its replication calls through the lifecycle replication_sink boundary (schedule_delete wrapper and the sink's ReplicationObjectBridge re-export), as the lifecycle guard requires.
- The ecstore public facade drops api::client: object_api_utils is exposed as api::object_api_utils, and the rustfs crate takes admin_handler_utils (AdminError) from rustfs-s3-client directly (new dependency).
- Guard updates: the migration guard no longer pins mod client in ecstore's lib.rs or the admin_handler_utils facade module (it pins the new api::object_api_utils facade instead), and the module-lint register follows object_api_utils.rs to its new path.

Verification: cargo check -p rustfs-ecstore --all-targets and -p rustfs; cargo fmt --all; tier/transition/lifecycle-focused nextest (626 passed) and the decommission/rebalance/heal families in a filtered run (603 passed; the full-suite parallel run only fails on this machine's known decommission/rebalance baseline flakes, which pass in filtered reruns and fail identically on pristine origin/main); layer/migration/s3s/logging/error-format/doc-path guard scripts all pass.

* docs(architecture): record the S3 client extraction and reword invariant 4 (#6669)

Closes the documentation step of rustfs/backlog#1842. ARCHITECTURE.md invariant 4 now states the serving-vs-consuming distinction the adversarial ruling asked for: ecstore must not serve HTTP/S3 wire types, while consuming remote S3 endpoints is a legitimate engine capability that lives in the extracted rustfs-s3-client crate. The violation note is updated from the pre-extraction snapshot (58 files, embedded client) to the current ratcheted state (shrink-only S3S_ECSTORE_FILES_BASELINE in scripts/check_s3s_footprint.sh, object_lock converted first), and the crate map gains s3-client. ecstore-module-split-plan.md gets the client-directory entry the plan was missing: a Current Shape row and a completed-extraction section describing the pure-move + shim + direct-import sequence and the re-homing of the two misfiled server-side modules.

crates/ecstore/src/set_disk/mod.rs

@@ -55,7 +55,6 @@ use crate::bucket::replication::{
 };
 use crate::bucket::versioning::VersioningApi;
 use crate::bucket::versioning_sys::BucketVersioningSys;
-use crate::client::{object_api_utils::get_raw_etag, transition_api::ObjectReader, transition_api::ReaderImpl};
 use crate::cluster::rpc::heal_bucket_local_on_disks;
 use crate::data_usage::record_compression_total_memory;
 use crate::diagnostics::get::{
@@ -88,6 +87,7 @@ use crate::error::{GenericError, ObjectApiError, is_err_object_not_found};
 use crate::io_support::bitrot::{create_bitrot_reader, create_bitrot_reader_from_bytes, create_bitrot_writer};
 use crate::object_api::ObjectOptions;
 use crate::object_api::get_object_body_cache_hook;
+use crate::object_api::object_api_utils::get_raw_etag;
 use crate::runtime::instance::{InstanceContext, bootstrap_ctx};
 use crate::runtime::sources as runtime_sources;
 use crate::services::batch_processor::AsyncBatchProcessor;
@@ -151,6 +151,7 @@ use rustfs_madmin::heal_commands::{HealDriveInfo, HealResultItem, Infos};
 use rustfs_object_capacity::capacity_scope::{
     CapacityScope, CapacityScopeDisk, current_dirty_generation, record_capacity_scope, record_global_dirty_scope,
 };
+use rustfs_s3_client::transition_api::{ObjectReader, ReaderImpl};
 use rustfs_s3_types::EventName;
 #[cfg(test)]
 use rustfs_utils::http::SSEC_ALGORITHM_HEADER;