New uv based workflow for PyRTL developers

[fdxmw]

Hello, if you're making changes to PyRTL, PR #476 made significant changes to the testing and documentation workflows.

Moving forward, you'll need to install uv, and run all PyRTL tests with:

$ uv run just tests

To generate Sphinx documentation:

$ uv run just docs

To run tests and generate documentation:

$ uv run just presubmit

It's a great idea to run uv run just presubmit before sending a pull request. PR #476 has more background and rationale for these changes. Let me know if you have any comments or questions!