fix(ecstore): optimize ObjectInfo clone and fix critical TODOs (#3149)

* fix(ecstore): optimize ObjectInfo clone and fix critical TODOs

## ObjectInfo hot-path clone optimization (issue #653 item 2)
- Wrap user_defined (HashMap), user_tags (String), parts (Vec) in Arc
- Clone cost reduced from ~20 heap allocations to O(1) ref count bump
- Updated 11 downstream access sites with explicit deref where needed

## Critical TODO/FIXME fixes (issue #653 item 7)
- rpc/peer_s3_client.rs: descriptive error message for empty peer response
- set_disk/write.rs: concurrent rollback deletes via tokio::spawn + join_all
- store_list_objects.rs: resolved FIXME with explanation + 4 regression tests
- store/bucket.rs: namespace write locks for make_bucket and delete_bucket

Skipped TODOs (too risky without broader context):
- multipart.rs:30 nslock — causes lock timeout in existing tests
- bucket.rs:88 cached list_bucket — needs cache invalidation strategy
- bucket.rs:149 replication delete — needs replication subsystem integration

1134 tests pass (1 flaky under parallel execution, passes individually).

* fix: address PR #3149 review comments

- Preserve NamespaceLockQuorumUnavailable variant in bucket create/delete
- Fix cancellation test to actually test cancellation (keep senders open)
- Update ObjectInfo consumers in app/ for Arc-backed fields
- Update bucket_usecase.rs user_tags to Arc<String>

* fix: update ObjectInfo Arc consumers

* fix: address ecstore merge review comments

* fix: cancel blocked merge output sends

* fix(ecstore): satisfy ObjectInfo clone clippy

crates/ecstore/src/rpc/peer_s3_client.rs

@@ -843,12 +843,13 @@ impl PeerS3Client for RemotePeerS3Client {
                 });
                 let response = client.make_bucket(request).await?.into_inner();
 
-                // TODO: deal with error
                 if !response.success {
                     return if let Some(err) = response.error {
                         Err(err.into())
                     } else {
-                        Err(Error::other(""))
+                        Err(Error::other(format!(
+                            "make_bucket({bucket}): peer returned failure without error details"
+                        )))
                     };
                 }