fix(storage): also remove the empty object directory when the xl.meta commit fails

The xl.meta rename at the end of RenameData creates the object directory
the same way the data rename does, and its failure branch left that
directory behind for writes without a data directory, such as inline
and zero-byte objects. Remove it and its empty parents there too, with
the same trailing-slash call that PR #286 adds to the data branch for
issue #285.

Making the cleanup safe against concurrent writes needs two more
changes:

- deleteFile now walks up with a trailing slash, so each parent step
  removes only an empty directory. Between two steps of a walk, another
  walk can remove the rest of the chain and a writer can commit an
  object whose xl.meta sits at the path the first walk removes next,
  for example the object "parent" under the key "parent/xl.meta/child".
  The walk used to delete that file. Ordinary deletes could already do
  this; the new cleanup made it reachable with failed writes.

- The two renames of RenameData retry when the directory creation or
  the rename reports "not found" while the source is still in place,
  up to once per path level. A late, failed RenameData can now remove
  the directory another write of the same key has just created, and
  that write used to fail on the drive although its data was intact.
  The retry decides on the error of the attempt itself, because another
  write can recreate the directories in between. renameAll's error
  mapping moves unchanged into renameAllErr so that the retry can see
  the raw error.

The stagedDataGoneDisks test helper now swaps the drives behind the
set's disk list under the lock that the list takes, instead of
replacing the getDisks callback that background tasks read unlocked.

Tests:
- TestXLStorageRenameDataCommitMetaMissingRemovesEmptyDirs: zero-byte
  and inline commit failures leave no empty directories, a sibling and
  a moved data directory stay.
- TestXLStorageWalkUpKeepsCommittedObject: a committed object at a
  parent path survives the walk, through DeleteVersion and both
  cleanup branches.
- TestRenameDataSurvivesConcurrentEmptyDirCleanup: PutObject (large
  and inline) and CompleteMultipartUpload succeed when a late failed
  RenameData of the same key removes their fresh directory on all 16
  drives.
- TestXLStorageRenameDataRetriesWhileCleanupWalksUp: a write survives
  a cleanup that removes each level of its path in turn, also when a
  nested-key write recreates the directories in between.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/os-reliable.go

@@ -142,32 +142,37 @@ func renameAll(srcFilePath, dstFilePath, baseDir string) (err error) {
 		return err
 	}
 
-	if err = reliableRename(srcFilePath, dstFilePath, baseDir); err != nil {
-		switch {
-		case isSysErrNotDir(err) && !osIsNotExist(err):
-			// Windows can have both isSysErrNotDir(err) and osIsNotExist(err) returning
-			// true if the source file path contains an non-existent directory. In that case,
-			// we want to return errFileNotFound instead, which will honored in subsequent
-			// switch cases
-			return errFileAccessDenied
-		case isSysErrPathNotFound(err):
-			// This is a special case should be handled only for
-			// windows, because windows API does not return "not a
-			// directory" error message. Handle this specifically here.
-			return errFileAccessDenied
-		case isSysErrCrossDevice(err):
-			return fmt.Errorf("%w (%s)->(%s)", errCrossDeviceLink, srcFilePath, dstFilePath)
-		case osIsNotExist(err):
-			return errFileNotFound
-		case osIsExist(err):
-			// This is returned only when destination is a directory and we
-			// are attempting a rename from file to directory.
-			return errIsNotRegular
-		default:
-			return err
-		}
+	return renameAllErr(reliableRename(srcFilePath, dstFilePath, baseDir), srcFilePath, dstFilePath)
+}
+
+// renameAllErr converts an error of reliableRename into the error that
+// renameAll returns.
+func renameAllErr(err error, srcFilePath, dstFilePath string) error {
+	switch {
+	case err == nil:
+		return nil
+	case isSysErrNotDir(err) && !osIsNotExist(err):
+		// Windows can have both isSysErrNotDir(err) and osIsNotExist(err) returning
+		// true if the source file path contains an non-existent directory. In that case,
+		// we want to return errFileNotFound instead, which will honored in subsequent
+		// switch cases
+		return errFileAccessDenied
+	case isSysErrPathNotFound(err):
+		// This is a special case should be handled only for
+		// windows, because windows API does not return "not a
+		// directory" error message. Handle this specifically here.
+		return errFileAccessDenied
+	case isSysErrCrossDevice(err):
+		return fmt.Errorf("%w (%s)->(%s)", errCrossDeviceLink, srcFilePath, dstFilePath)
+	case osIsNotExist(err):
+		return errFileNotFound
+	case osIsExist(err):
+		// This is returned only when destination is a directory and we
+		// are attempting a rename from file to directory.
+		return errIsNotRegular
+	default:
+		return err
 	}
-	return nil
 }
 
 // Reliably retries os.RenameAll if for some reason os.RenameAll returns