Update examples + check repository health

[mdpiper]

This PR started as a simple check on the example notebooks, but ended up including some general repository maintenance. The changes:

1. Dropped support for Python 3.9, added 3.13
2. Touched up example notebooks, added a launch notebook and a README
3. Replaced Mambaforge with Miniforge in the CI test workflow, also set an absolute path required for the latest bmi_tester
4. Applied updated formatting and linting rules from black and ruff

[mdpiper]

@mcflugen It looks like pre-commit is installed as a GitHub App, but there's no configuration for it. Would you like to ignore this for now, or maybe add it to this PR?

[mcflugen]

@mcflugen It looks like pre-commit is installed as a GitHub App, but there's no configuration for it. Would you like to ignore this for now, or maybe add it to this PR?

@mdpiper, I added that in #32. To make a cleaner pull request, I've moved those commits to #34.

[mcflugen]

👍