* craft-video: VP9 decoder from FilmCraft (`vp9-decode` feature)
FilmCraft's crates/vp9 at 4c0d2ad7 becomes craft_video::vp9::decode. The encoder moves to
vp9/encode and is still exported from craft_video::vp9. Feature vp9 now turns on vp9-decode and
vp9-encode, so either half can be built without the other.
The decoder's tests find ffmpeg and the fixture directory through craft-media-testkit; a fixture
that cannot be generated fails under CRAFT_MEDIA_REQUIRE_ORACLES=1. craft-video is built at
opt-level 3 in the dev profile, as FilmCraft built its codecs.
* craft-video: VP9 decoder checks its picture store against a memory budget
DeckCraft's copy of the decoder refuses a frame size whose pictures (eight reference slots, the
new frame and those in flight) would not fit a byte budget. The budget type comes with it as
craft_video::budget; FilmCraft's 2^26 luma sample cap stays.
