Improve performances of URL.joinpath

[bdraco]

• Avoid the slice for the common cases
• Avoid creating new lists
• Avoid reversing as long as possible so we do not have to insert at the front or create a new list since insert at 0 has O(n) time complexity, and append has O(1) time complexity

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.06%. Comparing base (14c3759) to head (8e5d0b4).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1418   +/-   ##
=======================================
  Coverage   96.06%   96.06%           
=======================================
  Files          31       31           
  Lines        5773     5774    +1     
  Branches      347      348    +1     
=======================================
+ Hits         5546     5547    +1     
  Misses        201      201           
  Partials       26       26           

Flag	Coverage Δ
CI-GHA	96.06% <100.00%> (+<0.01%)	⬆️
MyPy	48.69% <100.00%> (+<0.01%)	⬆️
OS-Linux	99.55% <100.00%> (+<0.01%)	⬆️
OS-Windows	99.62% <100.00%> (+<0.01%)	⬆️
OS-macOS	99.30% <100.00%> (+<0.01%)	⬆️
Py-3.10.11	99.28% <100.00%> (+<0.01%)	⬆️
Py-3.10.15	99.51% <100.00%> (+<0.01%)	⬆️
Py-3.11.10	99.51% <100.00%> (+<0.01%)	⬆️
Py-3.11.9	99.28% <100.00%> (+<0.01%)	⬆️
Py-3.12.7	99.51% <100.00%> (+<0.01%)	⬆️
Py-3.13.0	99.51% <100.00%> (+<0.01%)	⬆️
Py-3.9.13	99.24% <100.00%> (+<0.01%)	⬆️
Py-3.9.20	99.47% <100.00%> (+<0.01%)	⬆️
Py-pypy7.3.16	99.53% <100.00%> (+<0.01%)	⬆️
Py-pypy7.3.17	99.55% <100.00%> (+<0.01%)	⬆️
VM-macos-latest	99.30% <100.00%> (+<0.01%)	⬆️
VM-ubuntu-latest	99.55% <100.00%> (+<0.01%)	⬆️
VM-windows-latest	99.62% <100.00%> (+<0.01%)	⬆️
pytest	99.55% <100.00%> (+<0.01%)	⬆️

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[codspeed-hq]

CodSpeed Performance Report

Merging #1418 will improve performances by 21.15%

_{Comparing joinpath_perf (8e5d0b4) with master (14c3759)}

Summary

⚡ 4 improvements
✅ 81 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	joinpath_perf	Change
⚡	test_url_joinpath	787.1 µs	655.5 µs	+20.08%
⚡	test_url_joinpath_encoded	745 µs	614.9 µs	+21.15%
⚡	test_url_joinpath_encoded_long	1,090.7 µs	964.3 µs	+13.1%
⚡	test_url_joinpath_with_truediv	879.1 µs	750.9 µs	+17.08%