Save Video gets a bit_depth widget (auto/8-bit/10-bit). 'auto' preserves
the source file's bit depth when re-encoding; 10-bit encodes h264
yuv420p10le from 16-bit RGB frames so float-precision sources keep their
gradients instead of being quantized to 8-bit.
Video inputs can declare 10-bit support via Video.Input(accepts={"depth": 10}).
At input binding, videos bound to inputs without the declaration are
replaced with a copy whose saved files default to 8-bit, so existing nodes keep producing 8-bit files no matter the
source depth. SaveVideo and VideoSlice declare support, so trimming a
10-bit video and saving it keeps 10-bit.
Signed-off-by: bigcat88 <bigcat88@icloud.com>
