Use packaging for LegacyVersion / LooseVersion

[tony]

Ongoing issue:

• python 3.10 raises warnings with distutils

• In packaging, LegacyVersion (the supercessor to LooseVersion) will be deprecated, we won't be able to support 2.4-openbsd (like what is seen on OpenBSD's tmux versions

  This deprecation warning is live in 21.3 and looks like it will have LegacyVersion removed in 22

    /home/t/work/python/libtmux/.venv/lib/python3.10/site-packages/packaging/version.py:127: 
      DeprecationWarning: Creating a LegacyVersion has been deprecated and will be removed in the next major release
      warnings.warn(
  
  -- Docs: https://docs.pytest.org/en/stable/warnings.html
  

[codecov]

Codecov Report

Merging #349 (d556084) into master (5f66a68) will increase coverage by 0.19%.
The diff coverage is 100.00%.

❗ Current head d556084 differs from pull request most recent head 9306d46. Consider uploading reports for the commit 9306d46 to get more accurate results

@@            Coverage Diff             @@
##           master     #349      +/-   ##
==========================================
+ Coverage   87.68%   87.88%   +0.19%     
==========================================
  Files          20       16       -4     
  Lines        1852     1519     -333     
  Branches      298        0     -298     
==========================================
- Hits         1624     1335     -289     
- Misses        154      184      +30     
+ Partials       74        0      -74     

Impacted Files	Coverage Δ
libtmux/common.py	86.86% <100.00%> (ø)
tests/test_common.py	98.26% <100.00%> (+0.82%)	⬆️
tests/test_version.py	100.00% <100.00%> (ø)
tests/test_pane.py	100.00% <0.00%> (ø)
tests/test_server.py	100.00% <0.00%> (ø)
tests/test_tmuxobject.py	100.00% <0.00%> (ø)
src/libtmux/pytest_plugin.py
src/libtmux/test.py
src/libtmux/pane.py
src/libtmux/window.py
... and 22 more

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[tony]

Resolved via e3e6c39 (#351)