Improve benchmarks and single frame write path

[nhooyr]

Updates #62

[codecov]

Codecov Report

Merging #72 into master will decrease coverage by 0.06%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #72      +/-   ##
==========================================
- Coverage   80.51%   80.44%   -0.07%     
==========================================
  Files          10       10              
  Lines         662      670       +8     
==========================================
+ Hits          533      539       +6     
- Misses        109      111       +2     
  Partials       20       20

Impacted Files	Coverage Δ
websocket.go	80.97% <100%> (-0.15%)	⬇️
xor.go	100% <100%> (ø)	⬆️

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