Adds a second Linux decoder backend, crates/platform/src/nvdec, that talks to
NVIDIA's driver directly (libnvcuvid + the CUDA driver, both loaded at run
time). It is registered in front of VA-API: what NVDEC declines still reaches
VA-API, then the software decoders. H.264 8-bit and HEVC 8/10-bit, 4:2:0
progressive.
NVIDIA's parser takes Annex B access units, so there is no host-side DPB.
Pictures are read back as NV12 / P016 through the existing biplanar path and
are bit-exact with the software decoders. The CUDA context is the one
nvenc::device already retains; it gains push/pop and copy-to-host. A seek
recreates the parser and keeps the decoder.
Also fixes tests/setting.rs, which expected the Media Foundation backend name
on Linux, and updates the Hardware decoding tooltip and its Spanish row.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
03a840d28b