Pool buffers in wspb and wsjson

[nhooyr]

Closes #71

[codecov]

Codecov Report

Merging #85 into master will decrease coverage by 1.53%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master     #85      +/-   ##
=========================================
- Coverage   80.94%   79.4%   -1.54%     
=========================================
  Files          11      12       +1     
  Lines         871     879       +8     
=========================================
- Hits          705     698       -7     
- Misses        136     150      +14     
- Partials       30      31       +1

Impacted Files	Coverage Δ
internal/bpool/bpool.go	0% <0%> (ø)
websocket.go	75.89% <0%> (-1.57%)	⬇️

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