s/len/length/ s/cap/capacity/ to avoid builtin shadowing

[quasilyte]

No description provided.

[codecov]

Codecov Report

Merging #1292 into master will decrease coverage by 0.03%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #1292      +/-   ##
==========================================
- Coverage   74.31%   74.28%   -0.04%     
==========================================
  Files         254      254              
  Lines       11172    11172              
==========================================
- Hits         8303     8299       -4     
- Misses       2074     2078       +4     
  Partials      795      795

Impacted Files	Coverage Δ
transport/internet/udp/hub.go	78.08% <100%> (ø)	⬆️
proxy/vmess/encoding/commands.go	59.52% <66.66%> (ø)	⬆️
transport/internet/websocket/connection.go	66.03% <0%> (-7.55%)	⬇️
common/crypto/chunk.go	90.27% <0%> (-5.56%)	⬇️
proxy/vmess/inbound/inbound.go	75.91% <0%> (-1.58%)	⬇️
common/log/logger.go	87.5% <0%> (ø)	⬆️
common/task/task.go	76.28% <0%> (+1.03%)	⬆️
transport/internet/http/hub.go	76.31% <0%> (+2.63%)	⬆️
common/buf/reader.go	78.2% <0%> (+5.12%)	⬆️

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