optimization: MessageReader: use a static 4-byte buffer for header reads

Avoids an allocation per Message call.

Author: Noam Preil

arrow/ipc/message.go

@@ -150,6 +150,7 @@ type messageReader struct {
 	msg      *Message
 
 	mem memory.Allocator
+	header [4]byte
 }
 
 // NewMessageReader returns a reader that reads messages from an input stream.
@@ -188,7 +189,7 @@ func (r *messageReader) Release() {
 // underlying stream.
 // It is valid until the next call to Message.
 func (r *messageReader) Message() (*Message, error) {
-	buf := make([]byte, 4)
+	buf := r.header[:]
 	_, err := io.ReadFull(r.r, buf)
 	if err != nil {
 		return nil, fmt.Errorf("arrow/ipc: could not read continuation indicator: %w", err)