wsjson: Extend benchmark with multiple sizes

[qrvnl@dios ~/src/websocket] 130$ go test -bench=. ./wsjson/
goos: linux
goarch: amd64
pkg: nhooyr.io/websocket/wsjson
cpu: 12th Gen Intel(R) Core(TM) i5-1235U
BenchmarkJSON/json.Encoder/8-12         14041426            72.59 ns/op  110.21 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/16-12        13936426            86.99 ns/op  183.92 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/32-12        11416401           115.3 ns/op   277.59 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/128-12        4600574           264.7 ns/op   483.55 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/256-12        2710398           433.9 ns/op   590.06 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/512-12        1588930           717.3 ns/op   713.82 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/1024-12        823138          1484 ns/op     689.80 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/2048-12        402823          2875 ns/op     712.32 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/4096-12        213926          5602 ns/op     731.14 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/8192-12         92864         11281 ns/op     726.19 MB/s          16 B/op          1 allocs/op
BenchmarkJSON/json.Encoder/16384-12        39318         29203 ns/op     561.04 MB/s          19 B/op          1 allocs/op
BenchmarkJSON/json.Marshal/8-12         10768671           114.5 ns/op    69.89 MB/s          48 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/16-12        10140996           113.9 ns/op   140.51 MB/s          64 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/32-12         9211780           121.6 ns/op   263.06 MB/s          64 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/128-12        4632796           264.2 ns/op   484.53 MB/s         224 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/256-12        2441511           473.5 ns/op   540.65 MB/s         432 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/512-12        1298788           896.2 ns/op   571.27 MB/s         912 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/1024-12        602084          1866 ns/op     548.83 MB/s        1808 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/2048-12        341151          3817 ns/op     536.61 MB/s        3474 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/4096-12        175594          7034 ns/op     582.32 MB/s        6548 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/8192-12         83222         15023 ns/op     545.30 MB/s       13591 B/op          2 allocs/op
BenchmarkJSON/json.Marshal/16384-12        33087         39348 ns/op     416.39 MB/s       27304 B/op          2 allocs/op
PASS
ok      nhooyr.io/websocket/wsjson  32.934s