Expand CONTRIBUTING.md with development workflow details

[jtdub]

Description

The current CONTRIBUTING.md is approximately 50 lines and covers only basic setup. It lacks information that would help new contributors be productive.

Proposed Additions

1. How to run tests locally — pytest commands, how to run a single test, how to use pytest-xdist for parallel execution
2. How to run linting — Individual ruff, mypy, pyright, pylint commands (not just build.py lint-and-test)
3. Commit message conventions — What style to follow
4. PR expectations — What a good PR looks like, expected test coverage
5. Architecture orientation — Brief pointer to where different types of changes should go (new platform → platforms/, new rule type → models.py + driver_base.py, etc.)
6. IDE setup tips — Recommended extensions/settings for VS Code or PyCharm given the strict type checking