Support single serialization for broadcast messages in listeners

[codingchili]

When sending an event to multiple clients we can serialize it once at a higher level, and then write the same serialized buffer to multiple connections.

• [x] support binary transfer mode
• [x] support writing buffers in the websocket listener without any re-encoding.
• [ ] support writing Strings when not in binary transfer mode without any re-encoding.
• [ ] add support for preparing a response regardless of if binary transfer mode is enabled or not.

[codingchili]

When in text mode: strings are still created from buffers when writing. no action for now.