Instead of calling ParseHex, do the hex.Decode directly.
name old time/op new time/op delta
UnmarshalJSON-8 86.9ns ± 0% 42.6ns ± 0% -50.94% (p=0.000 n=15+14)
name old alloc/op new alloc/op delta
UnmarshalJSON-8 128B ± 0% 0B -100.00% (p=0.000 n=15+15)
name old allocs/op new allocs/op delta
UnmarshalJSON-8 2.00 ± 0% 0.00 -100.00% (p=0.000 n=15+15)
Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>