log: replace tmp with bytes.Buffer.AvailableBuffer

[ucwong]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 47.28%. Comparing base (e4e9a5c) to head (c2de451).
Report is 25 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1943      +/-   ##
==========================================
+ Coverage   47.25%   47.28%   +0.03%     
==========================================
  Files         568      568              
  Lines       68853    68852       -1     
==========================================
+ Hits        32534    32560      +26     
+ Misses      33794    33767      -27     
  Partials     2525     2525              

Files	Coverage Δ
log/format.go	62.89% <66.66%> (-0.17%)	⬇️

... and 10 files with indirect coverage changes