* craft-video: H.264 decoder from FilmCraft (`h264-decode` feature)
FilmCraft's crates/h264 at 4c0d2ad7 becomes craft_video::h264::decode. The encoder moves to
h264/encode and is still exported from craft_video::h264. Feature h264 now turns on h264-decode
and h264-encode, so either half can be built without the other.
Without the threads feature a reference row that was never published read through expect();
it now reads as a gray row. craft_video::budget (the picture memory budget from DeckCraft's
bitstream crate) is added for the next commit. craft-video is built at opt-level 3 in the dev
profile, as FilmCraft built its codecs.
* craft-video: H.264 decoder hardening from DeckCraft's copy
- The picture store (DPB, current picture, pictures in flight or queued for output) is checked
against a memory budget before a picture is allocated; Decoder::set_memory_budget.
- configure_avcc checks every entry before handling any: SPS NAL units in the first list, PPS in
the second. A picture slice in the record starts no picture.
- The inverse transforms clamp coefficients to the spec's r range instead of overflowing.
- Temporal direct motion vectors are scaled in i32 and clipped to the spec range.
- slice_qp_delta is added with a checked add.
- A picture job sets up its picture state inside the panic guard.
