build: Remove .coveragerc, use pyproject.toml

[tony]

See also: tmux-python/tmuxp#824

[codecov]

Codecov Report

Merging #443 (7183fd4) into master (79580eb) will increase coverage by 1.06%.
The diff coverage is n/a.

❗ Current head 7183fd4 differs from pull request most recent head e3f7c8e. Consider uploading reports for the commit e3f7c8e to get more accurate results

@@            Coverage Diff             @@
##           master     #443      +/-   ##
==========================================
+ Coverage   86.32%   87.38%   +1.06%     
==========================================
  Files          20       20              
  Lines        1821     1792      -29     
  Branches      277      270       -7     
==========================================
- Hits         1572     1566       -6     
+ Misses        170      154      -16     
+ Partials       79       72       -7     

Impacted Files	Coverage Δ
src/libtmux/session.py	76.43% <0.00%> (+1.01%)	⬆️
src/libtmux/window.py	78.10% <0.00%> (+1.09%)	⬆️
src/libtmux/common.py	84.11% <0.00%> (+1.92%)	⬆️
src/libtmux/pytest_plugin.py	81.08% <0.00%> (+2.13%)	⬆️
src/libtmux/test.py	76.59% <0.00%> (+2.36%)	⬆️
src/libtmux/pane.py	82.71% <0.00%> (+4.30%)	⬆️
conftest.py	92.00% <0.00%> (+6.81%)	⬆️

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