Fix volume.fsck -forcePurging -reallyDeleteFromVolume to fail fast on filer traversal errors (#8015)

* Add TraverseBfsWithContext and fix race conditions in error handling

- Add TraverseBfsWithContext function to support context cancellation
- Fix race condition in doTraverseBfsAndSaving using atomic.Bool and sync.Once
- Improve error handling with fail-fast behavior and proper error propagation
- Update command_volume_fsck to use error-returning saveFn callback
- Enhance error messages in readFilerFileIdFile with detailed context

* refactoring

* fix error format

* atomic

* filer_pb: make enqueue return void

* shell: simplify fs.meta.save error handling

* filer_pb: handle enqueue return value

* Revert "atomic"

This reverts commit 712648bc354b186d6654fdb8a46fd4848fdc4e00.

* shell: refine fs.meta.save logic

---------

Co-authored-by: Chris Lu <chris.lu@gmail.com>

weed/shell/command_fs_merge_volumes.go

@@ -109,9 +109,9 @@ func (c *commandFsMergeVolumes) Do(args []string, commandEnv *CommandEnv, writer
 	defer util_http.GetGlobalHttpClient().CloseIdleConnections()
 
 	return commandEnv.WithFilerClient(false, func(filerClient filer_pb.SeaweedFilerClient) error {
-		return filer_pb.TraverseBfs(commandEnv, util.FullPath(dir), func(parentPath util.FullPath, entry *filer_pb.Entry) {
+		return filer_pb.TraverseBfs(context.Background(), commandEnv, util.FullPath(dir), func(parentPath util.FullPath, entry *filer_pb.Entry) error {
 			if entry.IsDirectory {
-				return
+				return nil
 			}
 			for _, chunk := range entry.Chunks {
 				chunkVolumeId := needle.VolumeId(chunk.Fid.VolumeId)
@@ -141,6 +141,7 @@ func (c *commandFsMergeVolumes) Do(args []string, commandEnv *CommandEnv, writer
 					fmt.Printf("failed to update %s: %v\n", path, err)
 				}
 			}
+			return nil
 		})
 	})
 }