Release mp4forge 0.4.0

[bakgio]

Summary

This PR ships the mp4forge 0.4.0 release and rolls up the follow-up work that landed after 0.3.0.

Highlights

• expanded the probe surface with additive richer codec details, media-characteristics reporting, and lightweight probe controls
• added deterministic structured dump and psshdump JSON/YAML export, including field-level dump payload reporting
• expanded CLI path ergonomics across extract, dump, edit, and psshdump
• improved divide by deriving playlist signaling from probed metadata and adding first-class validation before writing output
• added optional serde support for reusable report types
• expanded checked-in real fixture coverage and added dedicated high-level fuzz targets
• bumped crate metadata, lockfiles, docs, and release notes to 0.4.0