moq-net: add per-track cache age (SUBSCRIBE_OK), reconcile draft field order, port timescale to js/net

[kixelated]

Summary

Adds a publisher-controlled cache age to Track (replacing the hard-coded 5s group-eviction window), announced in lite-05 SUBSCRIBE_OK so relays re-serve with the same window; each subscriber's stale window is clamped to it. Also reconciles the SUBSCRIBE_OK field order with the draft and ports timescale negotiation to js/net so JS↔Rust lite-05 is wire-compatible again.

Implements Publisher Cache from the moq-lite-05 draft (moq-dev/drafts#23): "max age, in ms, of the oldest group the publisher will retain," analogous to HTTP Cache-Control: max-age.

Cache age

• rs/moq-net model: MAX_GROUP_AGE → pub const DEFAULT_CACHE (5s). New Track.cache: Duration (default 5s, with_cache, manual Default, serde as integer-ms skipping default). evict_expired uses Track.cache. stale clamped to cache in TrackProducer::subscribe, TrackWeak::subscribe, TrackSubscriber::update.
• publisher/subscriber: publisher announces track.cache; subscriber stamps info.cache onto the reconstructed local Track.
• js/net: mirrored Track.cache + SUBSCRIBE_OK wire field.

SUBSCRIBE_OK field order (reconciled with the draft)

The draft orders the trailing fields Timescale, Cache, Compression, but the merged timescale impl (#1439) emitted Compression, Timescale. Per the draft, both Rust and JS now encode/decode Timescale, Cache, Compression. lite-05 is WIP/unreleased, so this additive + reorder needs no version bump.

Timescale port to js/net

PR #1439 added per-frame timestamps to the Rust moq-net wire but never touched js/net, leaving JS↔Rust lite-05 wire-incompatible. This PR:

• adds timescale to the JS SUBSCRIBE_OK, and
• has the JS group-stream reader consume the per-frame zigzag-delta timestamp varint when the negotiated timescale is non-zero, keeping frame framing in sync with a timestamped (Rust) publisher.

js/net doesn't yet surface or produce per-frame moq-net timestamps (it reads media timestamps from the container payload), so JS publishers advertise timescale = 0 and the decoded delta is read only to stay in sync. Fully surfacing/producing per-frame timestamps in JS (the js/hang container migration that Rust did across moq-mux) is a separate follow-up.

Open items for the draft author

• Duration Delta: draft PR Loop disk source #23 adds both Timestamp Delta and Duration Delta to FRAME, but the merged Rust impl (Add per-track timescale and frame timestamps to moq-lite #1439) only implements Timestamp Delta. This PR matches the shipped Rust wire (timestamp-delta only). The draft should either drop Duration Delta or it should be implemented in Rust first.

Test plan

• cargo test -p moq-net (350 pass) incl. cache_age_controls_eviction, stale_clamped_to_cache, cache_roundtrips_on_lite05, cache_absent_before_lite05
• cargo test -p hang (catalog round-trips unaffected; cache skipped at default)
• just rs check (clippy -D warnings + rustfmt)
• just js check + biome; bun test in js/net (149 pass) incl. updated SUBSCRIBE_OK round-trip (timescale + cache + compression) and integration tests

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(Written by Claude)