refactor(ecstore): extract the embedded S3 client into rustfs-s3-client (#6627)

The storage engine embedded a ~8.4K-line hand-written S3 HTTP client under crates/ecstore/src/client (rustfs/backlog#1842). That client is a legitimate engine capability — it consumes remote S3-compatible endpoints for ILM tier warm backends and transition targets — but it was misfiled inside the engine, dragging s3s/hyper wire types into ecstore and blocking ARCHITECTURE.md invariant 4.

This PR is the pure-move step: 21 modules move verbatim to the new crates/s3-client crate (rustfs-s3-client), and crates/ecstore/src/client/mod.rs becomes a re-export shim so every in-crate crate::client:: path keeps working. The two server-side modules that were historically misfiled under client/ — object_api_utils.rs and object_handlers_common.rs — stay in ecstore.

Three reverse dependencies from the client into engine internals are severed so the move can be pure:

- transition_api::ReaderImpl::ObjectBody held ecstore's GetObjectReader; the client only ever reads the body, so the variant now holds an ObjectReader newtype over Box<dyn AsyncRead + Send + Sync + Unpin> with the same read_all() surface. The single production construction site (set_disk transition upload) and the two engine-side consumers were adjusted.
- api_list/api_remove used ecstore's storage_api_contracts / object_api types; api_list now imports BucketInfo from rustfs-storage-api directly, and api_remove uses the client's own transition_api::ObjectInfo (only .name/.version_id were read; the error-path bucket name is now threaded as a parameter instead of read from the deleted objects).
- the api_put_object_streaming regression tests built a GetObjectReader by hand; they now wrap the duplex stream in ObjectReader::new.

Guard updates: the s3s footprint ratchet gains an ecstore-scoped counter (42 files, shrink-only, per rustfs/backlog#1842), the ecstore module-lint-blanket register follows the moved files into crates/s3-client so the blanket ratchet keeps covering them, the logging guardrail path pin follows transition_api.rs, and the ::other(format!) baseline is regenerated (moved call sites left ecstore).

Verification: cargo check -p rustfs-s3-client -p rustfs-ecstore; cargo nextest run -p rustfs-s3-client (43 passed) and -p rustfs-ecstore (4515/4523; the 8 failures reproduce identically on pristine origin/main on the same machine); cargo clippy --all-targets; scripts/check_layer_dependencies.sh, check_architecture_migration_rules.sh, check_s3s_footprint.sh, check_logging_guardrails.sh, check_error_other_format_ratchet.sh, check_doc_paths.sh, check_ci_paths_sync.sh all pass.

crates/ecstore/src/client/mod.rs

@@ -12,28 +12,16 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// #730: S3 client compatibility models are kept while ECStore callers move to narrower facades.
+// The S3-consuming client moved to the `rustfs-s3-client` crate
+// (rustfs/backlog#1842). This shim keeps `crate::client::*` paths working for
+// in-crate consumers during the migration window; it is deleted once every
+// consumer imports `rustfs_s3_client` directly. Only the two server-side
+// modules below (misfiled here historically) remain as real ecstore code.
+
+pub use rustfs_s3_client::{
+    admin_handler_utils, api_get_options, api_list, api_put_object, api_remove, api_s3_datatypes, credentials, provider_versions,
+    signer_error, transition_api,
+};
 
-pub mod admin_handler_utils;
-pub mod api_error_response;
-pub mod api_get_object;
-pub mod api_get_options;
-pub mod api_list;
-pub mod api_put_object;
-pub mod api_put_object_common;
-pub mod api_put_object_multipart;
-pub mod api_put_object_streaming;
-pub mod api_remove;
-pub mod api_s3_datatypes;
-pub mod api_stat;
-pub mod bucket_cache;
-pub mod checksum;
-pub mod constants;
-pub mod credentials;
 pub mod object_api_utils;
 pub mod object_handlers_common;
-pub(crate) mod provider_versions;
-pub(crate) mod runtime_sources;
-pub mod signer_error;
-pub mod transition_api;
-pub mod utils;