feat: hatchling build system, update workflows

[manzt]

Description

What was changed in this pull request?

• Migrates clodius to a hatching build system (pyproject.toml-only, no setup.py or setup.cfg)
• Updates GH Actions with separate workflows for linting/testing
• GH Action caches data/* (uses hash of .gitignore and get_test_data.sh as cache key)
• Pins cooler & numpy versions for compatability
• Consolidate flake8 config to just .flake8.

Why is it necessary?

Some much needed updates to use clodius in modern projects.

Fixes #___

Checklist

• [x] Unit tests added or updated
• [ ] Updated CHANGELOG.md
• [ ] Run black .

[manzt]

@nvictus pybbi didn't compile with 3.11 so I haven't included

[manzt]

Ready for review...

[manzt]

it might be worth thinking about breaking about the dependencies of clodius so modules can be installed separately in the future. e.g.,

pip install clodius[all]

vs.,

pip install clodius[cooler,bigbed]

[manzt]

The linting error yields real errors now for undeclared variables. not sure how to resolve.

[nvictus]

The linting error yields real errors now for undeclared variables. not sure how to resolve.

It's a broken function. Let's fix or remove it.