Fix for compatibility with pandas 1.5.x

[ghackebeil]

Addresses #36

• relaxes version constraint for pandas to include 1.5.x
  • avoid using groupby(...).apply(..., include_groups=False)
• extend tests to cover get_region_dispatch_summary
  • this was mainly to check that some other groupby statements weren't producing the pandas DeprecationWarning related to this include_groups keyword added in pandas 2.x

Test workflow changes:

• Update test matrix to include testing with pandas 1.x + numpy 1.x
• Adding setup-python action to fix issue in macos-latest builds where uv would always use python3.13 (no matter what python-version was enabled)
• Dropping python 3.8 testing since it is past EOL
• Adding python 3.13 testing (with a few excludes to avoid unrelated build failures)

[ghackebeil]

If it's okay with you, I'll also add another build parameter to test the project on both pandas 1.x and 2.x. I'll wait until I see "workflow approval" on this PR to modify the cicd.yml file and push those changes as well.

[ghackebeil]

@nick-gorman: Any chance you have a moment to approve this PR for test workflow?

[ghackebeil]

Figured out how to run the action workflows on my fork. Updated description with test workflow changes.