hang: re-emit deprecated CMAF timescale/trackId in catalog

[kixelated]

Summary

Older players parse CMAF timescale and trackId from explicit catalog fields. The current schema moves both into the base64 init segment, which breaks anything pinned to @moq/hang@0.2.4 or earlier — see the \$ZodError thrown by the deployed moq-pilot web client this afternoon, where the new publisher's catalog (init-only) failed validation against the old schema.

• rs/hang/src/catalog/container.rs: add timescale: Option<u32> and track_id: Option<u32> to Container::Cmaf, both #[deprecated] and skipped on serialize when None. They're accepted (and ignored) on deserialize so catalogs from either side round-trip.
• rs/moq-mux/src/import/fmp4.rs: populate both fields from trak.mdia.mdhd.timescale / trak.tkhd.track_id when constructing the CMAF container during fMP4 import. This is the path the publisher actually uses, so freshly-published catalogs now carry the legacy fields again.
• All other call sites use .. in the pattern or pass None (FFI fallback / tests).
• js/hang/src/catalog/container.ts: accept the deprecated fields as optional.

Serde's derive doesn't propagate #[deprecated] into its generated read/write code, and our one populating site uses struct-init syntax that doesn't trigger the lint either, so the workspace builds clean.

Test plan

• cargo build --workspace
• cargo test -p hang -p moq-mux (84 passed)
• After publish, confirm an old-version watcher (@moq/hang@0.2.4) can decode a CMAF catalog from the new publisher.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Run ID: b207f7dc-7533-4a79-809d-1d8b9993d3a2

📥 Commits

Reviewing files that changed from the base of the PR and between ececd8e and b1b13f6.

📒 Files selected for processing (8)

• js/hang/src/catalog/container.ts
• rs/hang/src/catalog/container.rs
• rs/moq-ffi/src/media.rs
• rs/moq-mux/src/catalog/producer.rs
• rs/moq-mux/src/container/hang.rs
• rs/moq-mux/src/export/fmp4.rs
• rs/moq-mux/src/import/fmp4.rs
• rs/moq-mux/src/import/test/mod.rs

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Walkthrough

This pull request extends the CMAF container variant with optional timescale and track_id metadata fields across the moq codebase. The TypeScript schema and Rust enum are expanded to accept these fields, which are extracted from MP4 track metadata during import and marked as deprecated since they duplicate values derivable from the init segment. The FFI layer explicitly handles conversions to control field visibility. All pattern matches for Container::Cmaf are updated to use resilient destructuring syntax ({ init, .. }) to accommodate the new optional properties without breaking existing behavior.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 54.55% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: re-emitting deprecated CMAF timescale/trackId fields for backward compatibility with older clients.
Description check	✅ Passed	The description is directly related to the changeset, explaining the backward compatibility problem and detailing all modifications across multiple files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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• Commit unit tests in branch backwards-compatible-cmaf

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• Commit simplified code in branch backwards-compatible-cmaf

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