tools/dav1d: add xxhash 3 muxer

Decoding times Chimera-AV1-8bit-1920x1080-6736kbps.ivf with 4 frame and 4 tile threads on a core i7-8550U (disabled turbo boost):

muxer	time in seconds	on b85fbf6a (md5 optimizations)
null	73.9	72.5 s
md5	181.5	99.8 s
xxh3	75.6	73.8 s

Decoding Chimera-AV1-10bit-1920x1080-6191kbps.ivf with 6frame and 4 tile threads on the apple m1:

muxer	time in seconds	on 2dca9b28 (md5 optimizations)
null	27.9 s	27.8 s
md5	219.6 s	105.9 s
xxh3	28.5 s	28.3 s