Implement an API to parse a Sequence Header OBU and return a struct filled with basic stream information

The idea is to get stream information before frame data is available by passing it the contents of ISOBMFF's av1C or Matroska's CodecPrivate.

The function should return a struct much like Dav1dPictureParameters. Profile, level and tier would be nice as well, but not a must. Timing information if available should also be in the struct, as you can feed dav1d_decode() OBUs that were not encapsulated in any container, or were encapsulated in Annex-B, and the library user has no way to get that information otherwise.

Metadata OBUs like HDR information could also be parsed by this same function, as they are meant to go alongside the Sequence Header, but it's also not a must.