buffer: inline copyImpl

[gurgunday]

copyImpl is only used here, and removing the extra function call speeds up the copy benchmarks locally, we might need to confirm with a CI benchmark

After:

./node benchmark/run.js --filter buffer-copy buffers
buffers/buffer-copy.js
buffers/buffer-copy.js n=6000000 partial="true" bytes=8: 40,825,618.66360032
buffers/buffer-copy.js n=6000000 partial="false" bytes=8: 41,791,921.40845294
buffers/buffer-copy.js n=6000000 partial="true" bytes=128: 40,704,446.8970532
buffers/buffer-copy.js n=6000000 partial="false" bytes=128: 38,294,338.26186785
buffers/buffer-copy.js n=6000000 partial="true" bytes=1024: 27,828,082.06061716
buffers/buffer-copy.js n=6000000 partial="false" bytes=1024: 24,339,227.99011219

Before:

./node benchmark/run.js --filter buffer-copy buffers
buffers/buffer-copy.js
buffers/buffer-copy.js n=6000000 partial="true" bytes=8: 39,895,661.939214684
buffers/buffer-copy.js n=6000000 partial="false" bytes=8: 40,859,281.86584237
buffers/buffer-copy.js n=6000000 partial="true" bytes=128: 39,967,670.68408592
buffers/buffer-copy.js n=6000000 partial="false" bytes=128: 37,919,704.05339453
buffers/buffer-copy.js n=6000000 partial="true" bytes=1024: 27,719,259.341390397
buffers/buffer-copy.js n=6000000 partial="false" bytes=1024: 23,589,654.098257538

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.58%. Comparing base (2bda7cb) to head (1f9abbe).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #60396      +/-   ##
==========================================
+ Coverage   88.56%   88.58%   +0.01%     
==========================================
  Files         704      704              
  Lines      207774   207767       -7     
  Branches    40025    40023       -2     
==========================================
+ Hits       184022   184054      +32     
+ Misses      15807    15762      -45     
- Partials     7945     7951       +6     

Files with missing lines	Coverage Δ
lib/buffer.js	100.00% <100.00%> (ø)

... and 41 files with indirect coverage changes

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[gurgunday]

Just realized we use this convention quite a lot, this is probably not worth it