Small cleanups to making children paths

[bdraco]

What do these changes do?

This function was a bit hard to unpack so I have added some comments about what is going on.

Since we reconstruct nearly everything, create a new tuple instead of replacing

[codspeed-hq]

CodSpeed Performance Report

Merging #1304 will improve performances by 50.85%

_{Comparing make_child (2664612) with master (fa83191)}

Summary

⚡ 1 improvements
✅ 64 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	make_child	Change
⚡	test_url_joinpath_encoded	1,313.9 µs	871 µs	+50.85%

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.37%. Comparing base (fa83191) to head (2664612).
Report is 146 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1304      +/-   ##
==========================================
+ Coverage   95.90%   99.37%   +3.47%     
==========================================
  Files          27       19       -8     
  Lines        5323     4345     -978     
  Branches      320      270      -50     
==========================================
- Hits         5105     4318     -787     
+ Misses        192       22     -170     
+ Partials       26        5      -21     

Flag	Coverage Δ
CI-GHA	99.30% <100.00%> (+3.40%)	⬆️
MyPy	?
OS-Linux	99.30% <100.00%> (+<0.01%)	⬆️
OS-Windows	99.36% <100.00%> (+<0.01%)	⬆️
OS-macOS	99.03% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	99.01% <100.00%> (+<0.01%)	⬆️
Py-3.10.15	99.26% <100.00%> (+<0.01%)	⬆️
Py-3.11.10	99.26% <100.00%> (+<0.01%)	⬆️
Py-3.11.9	99.01% <100.00%> (+<0.01%)	⬆️
Py-3.12.7	99.26% <100.00%> (+<0.01%)	⬆️
Py-3.13.0	99.26% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	98.96% <100.00%> (+<0.01%)	⬆️
Py-3.9.20	99.21% <100.00%> (+<0.01%)	⬆️
Py-pypy7.3.16	99.26% <100.00%> (+<0.01%)	⬆️
Py-pypy7.3.17	99.29% <100.00%> (+<0.01%)	⬆️
VM-macos-latest	99.03% <100.00%> (+<0.01%)	⬆️
VM-ubuntu-latest	99.30% <100.00%> (+<0.01%)	⬆️
VM-windows-latest	99.36% <100.00%> (+<0.01%)	⬆️
pytest	99.30% <100.00%> (+<0.01%)	⬆️

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[bdraco]

Didn't expect it to speed up that much. Should do join as well

[bdraco]

I couldn't believe ._replace was so expensive, but it is

[bdraco]

origin, join, extend_query and with_path are probably good candidates to rework to avoid _replace. The others are likely not called enough that they are worth optimizing