Revert adding src to pytest pythonpath

[bdraco]

This turned out to not be needed from #22 and __init__.py file should have been added to the tests instead to always ensure we are testing the installed version.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.98%. Comparing base (d0f4e07) to head (85e884b).
Report is 63 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #27      +/-   ##
==========================================
+ Coverage   84.86%   85.98%   +1.12%     
==========================================
  Files          14       20       +6     
  Lines         555      678     +123     
  Branches       50       50              
==========================================
+ Hits          471      583     +112     
- Misses         66       68       +2     
- Partials       18       27       +9     

Flag	Coverage Δ
CI-GHA	85.69% <ø> (+0.82%)	⬆️
MyPy	68.92% <ø> (ø)
OS-Linux	98.73% <ø> (+3.32%)	⬆️
OS-Windows	92.85% <ø> (ø)
OS-macOS	96.62% <ø> (+3.76%)	⬆️
Py-3.10.11	96.20% <ø> (+3.34%)	⬆️
Py-3.10.15	97.89% <ø> (+2.99%)	⬆️
Py-3.11.10	97.89% <ø> (+2.99%)	⬆️
Py-3.11.9	96.20% <ø> (+3.34%)	⬆️
Py-3.12.6	97.48% <ø> (+2.58%)	⬆️
Py-3.13.0-rc.3	97.48% <ø> (+2.58%)	⬆️
Py-3.8.10	96.20% <ø> (+3.34%)	⬆️
Py-3.8.18	97.89% <ø> (+2.99%)	⬆️
Py-3.9.13	96.20% <ø> (+3.34%)	⬆️
Py-3.9.20	97.89% <ø> (+2.99%)	⬆️
Py-pypy7.3.11	94.38% <ø> (ø)
Py-pypy7.3.16	94.38% <ø> (ø)
Py-pypy7.3.17	94.38% <ø> (ø)
VM-macos-latest	96.62% <ø> (+3.76%)	⬆️
VM-ubuntu-latest	98.73% <ø> (+3.32%)	⬆️
VM-windows-latest	92.85% <ø> (ø)
pytest	98.56% <ø> (+3.15%)	⬆️

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