Fix issue #418. Unpin pymbolic. Resolve pydantic deprecation warnings

[huard]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes Params is_symbolic failing on linux #418
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• CHANGELOG.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• Unpin pymbolic
• Resolve issue with pymbolic > 2022.2
• Tweaks to silence pydantic DeprecationWarning

Does this PR introduce a breaking change?

Python3.9 support has been dropped.

Other information:

[Zeitsperre]

@huard If you want to implement a drop of Python3.9 in order to address the problem, go for it. We've been progressively dropping that version in a few places already.

[coveralls]

coverage: 81.279% (-0.07%) from 81.352%
when pulling ede6f94 on fix-418
into 57b7df4 on master.

[Zeitsperre]

LGTM!

A few final changes:

• In .pre-commit.config.yml, change the pyupgrade hook to py310-plus
• In pyproject.toml, change the ruff and isort configs to use "310" instead of "39", and drop py39 from black.

The remaining formatting should be automated by pre-commit.