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/s3-client/src/admin_handler_utils.rs

@@ -0,0 +1,47 @@
+// Copyright 2024 RustFS Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use http::status::StatusCode;
+use std::fmt::{self, Display, Formatter};
+
+#[derive(Default, thiserror::Error, Debug, Clone, PartialEq)]
+pub struct AdminError {
+    pub code: String,
+    pub message: String,
+    pub status_code: StatusCode,
+}
+
+impl Display for AdminError {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{}", self.message)
+    }
+}
+
+impl AdminError {
+    pub fn new(code: &str, message: &str, status_code: StatusCode) -> Self {
+        Self {
+            code: code.to_string(),
+            message: message.to_string(),
+            status_code,
+        }
+    }
+
+    pub fn msg(message: &str) -> Self {
+        Self {
+            code: "InternalError".to_string(),
+            message: message.to_string(),
+            status_code: StatusCode::INTERNAL_SERVER_ERROR,
+        }
+    }
+}