Small performance improvements to checking for chars in paths

[bdraco]

What do these changes do?

Replace startswith with single char checks
startswith: 0.005655332934111357
single char check: 0.0019642498809844255

Are there changes in behavior for the user?

no

[bdraco]

There is also an endswith that could be optimized but its rare to hit it

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.42%. Comparing base (eaf7641) to head (edec9fa).
Report is 271 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1143   +/-   ##
=======================================
  Coverage   95.42%   95.42%           
=======================================
  Files          30       30           
  Lines        4767     4767           
  Branches      423      423           
=======================================
  Hits         4549     4549           
  Misses        192      192           
  Partials       26       26           

Flag	Coverage Δ
CI-GHA	95.38% <100.00%> (ø)
MyPy	41.14% <100.00%> (ø)
OS-Linux	99.39% <100.00%> (ø)
OS-Windows	99.49% <100.00%> (ø)
OS-macOS	99.11% <100.00%> (ø)
Py-3.10.11	99.00% <100.00%> (ø)
Py-3.10.14	99.24% <100.00%> (ø)
Py-3.11.9	99.24% <100.00%> (ø)
Py-3.12.5	99.24% <100.00%> (ø)
Py-3.13.0-rc.2	99.24% <100.00%> (ø)
Py-3.8.10	98.95% <100.00%> (ø)
Py-3.8.18	99.18% <100.00%> (ø)
Py-3.9.13	98.95% <100.00%> (ø)
Py-3.9.19	99.18% <100.00%> (ø)
Py-pypy7.3.11	99.24% <100.00%> (ø)
Py-pypy7.3.16	99.24% <100.00%> (ø)
Py-pypy7.3.17	99.27% <100.00%> (ø)
VM-macos-latest	99.11% <100.00%> (ø)
VM-ubuntu-latest	99.39% <100.00%> (ø)
VM-windows-latest	99.49% <100.00%> (ø)
pytest	99.39% <100.00%> (ø)

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