[codex] Add zero-copy frame bytes

[kixelated]

Summary

• Add moq_net::AsBytes so owned Bytes, BytesMut, Vec, and String inputs can keep their allocation while borrowed byte inputs copy explicitly.
• Store whole-frame Bytes directly in FrameProducer, while partial writes and BufMut receive paths still use a mutable frame buffer.
• Thread owned Bytes through moq-mux whole-frame importers and selected web-transport write paths.
• Apply formatter output required by just check and fix two broken moq-native rustdoc links.

Public API changes

• Adds public moq_net::AsBytes.
• Changes FrameProducer::write, GroupProducer::{write_frame, write_frame_now}, and TrackProducer::{write_frame, write_frame_now} from Into to AsBytes.
• Changes moq-mux whole-frame importer decode methods for AAC, Opus, VP8, VP9, legacy, and import::Track from &[u8] to AsBytes.

Breaking change note

This can be source-breaking for custom caller buffer types that implemented Into but do not implement AsBytes. Common inputs remain covered: Bytes, BytesMut, Vec, String, &str, &[u8], &[u8; N], and borrowed owned buffers.

Validation

• just check

(Written by Codex)