- rational: store num/den natively instead of AVRational; math operators
re-implemented natively (ported av_reduce/av_d2q/av_cmp_q semantics,
verified bit-exact against FFmpeg)
- AudioParams: replace AVChannelLayout member with a plain uint64_t mask
(new render/channellayout.h constants mirror AV_CH_LAYOUT_* values)
- Timecode: native rescale (av_rescale_q/av_rescale_q_rnd equivalents)
with 128-bit intermediate precision
- core no longer finds or links FFMPEG::avutil
Part of the FFmpeg isolation effort: all FFmpeg access is being moved
behind a dedicated shared library (ffmpeg_bridge).
Mike-Solar