Improve Raven highlighting, docs, and CI

[martian56]

What changed

• make GitHub render Raven source with Rust highlighting
• use Rust fences for Raven examples in the README
• refresh install versions and CI presentation where needed
• modernize CI with current actions, explicit permissions, timeouts, and documentation checks

Why

GitHub does not recognize Raven yet. These changes give source files and examples readable highlighting while making the repository easier to trust, install, and maintain.

Validation

• rvpm fmt --check
• rvpm build
• rvpm test
• rvpm doc