Reduce allocations (#17584)

* Reduce allocations

* Add stringsHasPrefixFold which can compare string prefixes, while ignoring case and not allocating.
* Reuse all msgp.Readers
* Reuse metadata buffers when not reading data.

* Make type safe. Make buffer 4K instead of 8.

* Unslice

cmd/lock-rest-server.go

@@ -73,7 +73,7 @@ func (l *lockRESTServer) IsValid(w http.ResponseWriter, r *http.Request) bool {
 
 func getLockArgs(r *http.Request) (args dsync.LockArgs, err error) {
 	dec := msgpNewReader(io.LimitReader(r.Body, 1000*humanize.KiByte))
-	defer readMsgpReaderPool.Put(dec)
+	defer readMsgpReaderPoolPut(dec)
 	err = args.DecodeMsg(dec)
 	return args, err
 }