perf: adds AVX2 optimization for WebSocket masking

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Before

Benchmark_mask/amd64/wdvxdr1123-asm/8-12        444599608                2.711 ns/op    2951.47 MB/s           0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/16-12               414228843                2.908 ns/op    5501.26 MB/s           0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/32-12               405062330                2.916 ns/op    10974.92 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/128-12              323147343                3.702 ns/op    34575.47 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/256-12              181181568                6.595 ns/op    38815.81 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/512-12              134261024                8.932 ns/op    57323.30 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/1024-12             87677349                13.57 ns/op     75469.43 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/2048-12             49833375                24.09 ns/op     85028.41 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/4096-12             24303784                49.48 ns/op     82783.45 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/8192-12             12023418               100.2 ns/op      81742.79 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/16384-12             6031188               197.7 ns/op      82860.28 MB/s          0 B/op          0 allocs/op

After

Benchmark_mask/amd64/wdvxdr1123-asm/8-12        419437528                2.896 ns/op    2762.68 MB/s           0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/16-12               365261996                3.265 ns/op    4900.24 MB/s           0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/32-12               365955547                3.274 ns/op    9775.18 MB/s           0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/128-12              295290266                4.057 ns/op    31550.39 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/256-12              293986858                4.070 ns/op    62905.39 MB/s          0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/512-12              244795381                4.893 ns/op    104638.32 MB/s         0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/1024-12             162367981                7.413 ns/op    138135.75 MB/s         0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/2048-12             89116902                13.52 ns/op     151521.17 MB/s         0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/4096-12             46351291                25.72 ns/op     159256.73 MB/s         0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/8192-12             23834427                50.61 ns/op     161874.64 MB/s         0 B/op          0 allocs/op
Benchmark_mask/amd64/wdvxdr1123-asm/16384-12            12019286                99.17 ns/op     165210.00 MB/s         0 B/op          0 allocs/op