Allow reading frames into user-provided buffer to avoid allocations

Hi!

I’m trying to eliminate memory allocations when using my websocket handler, but read_frame currently allocates a new Vec for (almost) every incoming frame.

Would it be possible to provide an API variant that lets users supply a buffer to read into, avoiding these allocations? Or do you know of any workaround for this issue?

Start by locating the read_frame entry point and trace where each incoming frame's Vec is allocated. Review the current public API and frame-reading tests, if present, then determine the buffer variant's ownership and reuse behavior. Done means callers can read frames into a user-provided buffer without the per-frame allocation, with coverage for the new API.

Written by the indexing model from the issue text.