fix: improve bucket deletes we were leaving behind few files (#13364)

bucket deletes should purge entire bucket metadata
appropriately, use rename() to move the metadata files
to trash folder,

for dangling buckets instead of doing recursive deletes,
rename such buckets to trash folder as well.

Bonus: reduce retry duration for listing to 200ms

cmd/metacache-set.go

@@ -364,7 +364,7 @@ func (er *erasureObjects) streamMetadataParts(ctx context.Context, o listPathOpt
 			retries = 1
 		}
 
-		const retryDelay = 500 * time.Millisecond
+		const retryDelay = 250 * time.Millisecond
 		// All operations are performed without locks, so we must be careful and allow for failures.
 		// Read metadata associated with the object from a disk.
 		if retries > 0 {