Fix tests and minor updates

[avylove]

Deprecated pytest-xdist option

Most of the tests are currently broken because pytest-xdist deprecated looponfail without an alternative. Since we have filterwarnings = error this causes the deprecation warning to be treated as a failure. Rather than pin pytest-xdist or figure out how to filter the deprecation, I thought it was easier to remove it.

pytest-dev/pytest-xdist#826

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Test Updates

While I was in there, I moved the main test version to 3.10 and added 3.11 and 3.12-dev. 3.12-dev isn't currently available in the pipelines since 3.12 alpha 1 was released 2 days ago, but should be soon. It's tagged as optional.

The optional test syntax also seems to have changed, so I had to add continue-on-error. It's buggy in that it will show a success in the Actions view when a optional test fails, but the commit view still shows an X.

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SupportsIndex

After some back and forth with the Pylint team, I realized using int(width) instead of width__index__() for the formatting methods was actually wrong. The latest Pylint handles this correctly and I added a commit to revert to the previous behavior. Also noticed one of the typing files was using int instead of SupportsIndex, so updated that too.

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Other
Also made a handful of code tweaks, nothing significant.

[codecov]

Codecov Report

Base: 95.35% // Head: 95.15% // Decreases project coverage by -0.19% ⚠️

Coverage data is based on head (204a443) compared to base (df28567).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #244      +/-   ##
==========================================
- Coverage   95.35%   95.15%   -0.20%     
==========================================
  Files           9        9              
  Lines        1011     1011              
  Branches      176      215      +39     
==========================================
- Hits          964      962       -2     
- Misses         43       45       +2     
  Partials        4        4              

Impacted Files	Coverage Δ
blessed/sequences.py	100.00% <100.00%> (ø)
blessed/terminal.py	97.81% <0.00%> (-0.44%)	⬇️

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[avylove]

3.12-dev is available now, currently alpha1, and it looks like we're passing.

[avylove]

@jquast Can you approve this or give me access to approve my own PRs? The CI tests have been broken for the last couple months and it would be good to see them green again.