s3: fix remote object not caching (#7790)

* s3: fix remote object not caching

* s3: address review comments for remote object caching

- Fix leading slash in object name by using strings.TrimPrefix
- Return cached entry from CacheRemoteObjectToLocalCluster to get updated local chunk locations
- Reuse existing helper function instead of inline gRPC call

* s3/filer: add singleflight deduplication for remote object caching

- Add singleflight.Group to FilerServer to deduplicate concurrent cache operations
- Wrap CacheRemoteObjectToLocalCluster with singleflight to ensure only one
  caching operation runs per object when multiple clients request the same file
- Add early-return check for already-cached objects
- S3 API calls filer gRPC with timeout and graceful fallback on error
- Clear negative bucket cache when bucket is created via weed shell
- Add integration tests for remote cache with singleflight deduplication

This benefits all clients (S3, HTTP, Hadoop) accessing remote-mounted objects
by preventing redundant cache operations and improving concurrent access performance.

Fixes: https://github.com/seaweedfs/seaweedfs/discussions/7599

* fix: data race in concurrent remote object caching

- Add mutex to protect chunks slice from concurrent append
- Add mutex to protect fetchAndWriteErr from concurrent read/write
- Fix incorrect error check (was checking assignResult.Error instead of parseErr)
- Rename inner variable to avoid shadowing fetchAndWriteErr

* fix: address code review comments

- Remove duplicate remote caching block in GetObjectHandler, keep only singleflight version
- Add mutex protection for concurrent chunk slice and error access (data race fix)
- Use lazy initialization for S3 client in tests to avoid panic during package load
- Fix markdown linting: add language specifier to code fence, blank lines around tables
- Add 'all' target to Makefile as alias for test-with-server
- Remove unused 'util' import

* style: remove emojis from test files

* fix: add defensive checks and sort chunks by offset

- Add nil check and type assertion check for singleflight result
- Sort chunks by offset after concurrent fetching to maintain file order

* fix: improve test diagnostics and path normalization

- runWeedShell now returns error for better test diagnostics
- Add all targets to .PHONY in Makefile (logs-primary, logs-remote, health)
- Strip leading slash from normalizedObject to avoid double slashes in path

---------

Co-authored-by: chrislu <chris.lu@gmail.com>
Co-authored-by: Chris Lu <chrislusf@users.noreply.github.com>

weed/s3api/s3api_server.go

@@ -70,7 +70,7 @@ type S3ApiServer struct {
 	inFlightDataSize      int64
 	inFlightUploads       int64
 	inFlightDataLimitCond *sync.Cond
-	embeddedIam           *EmbeddedIamApi // Embedded IAM API server (when enabled)
+	embeddedIam *EmbeddedIamApi // Embedded IAM API server (when enabled)
 }
 
 func NewS3ApiServer(router *mux.Router, option *S3ApiServerOption) (s3ApiServer *S3ApiServer, err error) {