Reduce memcpy with chunked encoding

[bdraco]

finishing a chunk has a lot of memcpy. We can switch it to a b"".join() since it has a more efficient implementation in https://github.com/python/cpython/blob/91f4908798074db6c41925b4417bee1f933aca93/Objects/stringlib/join.h#L36 vs constructing a new bytes string for every add operation

[codspeed-hq]

CodSpeed Performance Report

Merging #9838 will improve performances by 21.36%

_{Comparing avoid_mem_cpy_chunks (636206a) with master (32ccfc9)}

Summary

⚡ 1 improvements
✅ 22 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	avoid_mem_cpy_chunks	Change
⚡	test_one_hundred_get_requests_with_512kib_chunked_payload[pyloop]	262.3 ms	216.1 ms	+21.36%

[bdraco]

Maybe we should use writelines

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.70%. Comparing base (32ccfc9) to head (636206a).

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9838      +/-   ##
==========================================
- Coverage   98.70%   98.70%   -0.01%     
==========================================
  Files         118      118              
  Lines       36148    36145       -3     
  Branches     4294     4294              
==========================================
- Hits        35680    35677       -3     
  Misses        315      315              
  Partials      153      153              

Flag	Coverage Δ
CI-GHA	98.59% <100.00%> (-0.01%)	⬇️
OS-Linux	98.27% <100.00%> (-0.01%)	⬇️
OS-Windows	96.07% <100.00%> (-0.01%)	⬇️
OS-macOS	97.36% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	97.20% <100.00%> (-0.01%)	⬇️
Py-3.10.15	97.76% <100.00%> (-0.01%)	⬇️
Py-3.11.10	97.80% <100.00%> (-0.05%)	⬇️
Py-3.11.9	97.26% <100.00%> (+<0.01%)	⬆️
Py-3.12.7	98.35% <100.00%> (-0.01%)	⬇️
Py-3.13.0	98.33% <100.00%> (+0.05%)	⬆️
Py-3.9.13	97.12% <100.00%> (-0.01%)	⬇️
Py-3.9.20	97.68% <100.00%> (-0.05%)	⬇️
Py-pypy7.3.16	97.29% <100.00%> (-0.01%)	⬇️
VM-macos	97.36% <100.00%> (+<0.01%)	⬆️
VM-ubuntu	98.27% <100.00%> (-0.01%)	⬇️
VM-windows	96.07% <100.00%> (-0.01%)	⬇️

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[bdraco]

#9839 is likely going to be a better solution

[bdraco]

replaced by #9839