mem: Avoid clearing new buffers and clear buffers from simpleBufferPools

[arjan-bal]

RELEASE NOTES:

• mem:
  • Avoid clearing buffers which newly allocated.
  • Clear large buffers (> 1MB) before re-using.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.05%. Comparing base (f448a97) to head (c237d60).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8670      +/-   ##
==========================================
+ Coverage   81.97%   83.05%   +1.08%     
==========================================
  Files         417      417              
  Lines       40788    32296    -8492     
==========================================
- Hits        33435    26823    -6612     
+ Misses       5991     4093    -1898     
- Partials     1362     1380      +18     

Files with missing lines	Coverage Δ
mem/buffer_pool.go	100.00% <100.00%> (ø)

... and 363 files with indirect coverage changes

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