Add AV1 codec support (av01/av1C boxes)

[thexeos]

Parse and write av01 sample entry and av1C configuration box per AV1-ISOBMFF binding spec. Adds MediaType::AV1, Av1Config, reader/writer integration in stsd/track/mp4copy, and integration test against a real AV1+AAC sample file.

Closes #139

[alfg]

Hey @thexeos, thanks for the contribution. If you could check out the clippy errors when you have a chance, please.

cargo clippy --all-targets --all-features

[Copilot]

Pull request overview

Adds AV1 (av01/av1C) support to the MP4 parser/writer so AV1 tracks can be detected, parsed from stsd, and exercised via tests and the mp4copy example (closes #139).

Changes:

• Introduce MediaType::AV1 and MediaConfig::Av1Config wiring through track read/write paths.
• Add parsing/writing for av01 sample entry and av1C configuration box.
• Add an integration test reading a real AV1+AAC MP4 sample, plus update mp4copy to recognize AV1.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/lib.rs	Adds integration test asserting AV1 track parsing from a real sample file.
src/types.rs	Adds MediaType::AV1 and Av1Config / MediaConfig::Av1Config variants.
src/track.rs	Detects AV1 tracks from stsd.av01 and supports writing AV1 sample entries.
src/mp4box/stsd.rs	Extends stsd to read/write an av01 sample entry.
src/mp4box/mod.rs	Registers av01/av1C box types and exposes Av01Box.
src/mp4box/av01.rs	Implements Av01Box and Av1CBox read/write + unit tests.
examples/mp4copy.rs	Adds AV1 handling when copying tracks.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.