CMAF passthrough attempt v2

[kixelated]

Replaces #822

Overview:

1. Added support for --passthrough (Rust only) when using HLS and fMP4 import to write the raw MP4 bytes.
2. MSE is a separate Backend, so it will be tree-shaken when not used.
   • The same but reverse for WebCodecs. No need for a fMP4 encoder.
3. The <hang-watch> element takes either a <video> or <canvas> tag to switch between backends.
   • Won't tree-shake, use the JS API if you want to reduce the bundle size.
4. Watch.Broadcast no longer owns the video/audio component; they have to be constructed separately.
   • Allows tree-shaking Watch.Audio.Source and Watch.Video.Source.
   • Opens the door for more tree-shakable modules that take a Broadcast.
5. Removed support for the unused raw container.
   • In hind-sight, a new container format should use delta encoded timestamps anyway.
   • Additionally, timestamps are being added to the moq-lite layer that we could reuse.
   • Sorry @gdavila, I didn't think enough before filing that issue.
6. The "mse" container contains an init_track, used to initialize the decoder.
   • This is inlined in the CMSF draft, but I plan to use it via a separate track for HLS fallback.
   • It's more efficient this way when renditions share an init segment.
7. A bunch of API changes to support the generic Backend interface.
   • ex. watch.audio.muted instead of watch.muted.

TODO:

• WebCodecs support for CMAF (decode MP4)
• MSE support for hang (encode MP4)
• Fix fMP4 import --passthrough not working with bbb
• Fix the buffering signal
• Fix the stats panel
• Actually review the HLS import changes
• Send jitter in the catalog so we can increase the latency on demand?
• Remove init_track and build it in memory instead?