rivet-container 0.2.0

Clean-room container demux (MP4/MKV/TS/AVI) and mux (AV1 MP4, CMAF, HLS) for the rivet transcoder, no FFmpeg. Imported as `container`.
Documentation 
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// No tests were present in the original demux/audio.rs.
// Add audio-extraction unit tests here as coverage is added.