Simplify testing minimum direct dependencies

[tjkuson]

Instead of defining a pytest-min dependency group to test against the lowest supported dependencies (which needs to be maintained), configure tox to use uv's lowest-direct resolution strategy to achieve the same thing.

Rename the test env to be more accurate (it's not just pytest minimum dependencies it checks). Prefixing with py310 means tox -e py310-lower-bounds will use Python 3.10 instead of relying on the gh-actions configuration.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.50%. Comparing base (01ff313) to head (23c624f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1528   +/-   ##
=======================================
  Coverage   94.50%   94.50%           
=======================================
  Files           2        2           
  Lines         510      510           
  Branches       62       62           
=======================================
  Hits          482      482           
  Misses         22       22           
  Partials        6        6           

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[seifertm]

Very nice! This also avoids having to maintain the minimum supported pytest version in multiple places.