Merge branch 'ps/ci-rust'

Merge branch 'ps/ci-rust'

CI improvements to handle the recent Rust integration better.

* ps/ci-rust:
  rust: support for Windows
  ci: verify minimum supported Rust version
  ci: check for common Rust mistakes via Clippy
  rust/varint: add safety comments
  ci: check formatting of our Rust code
  ci: deduplicate calls to `apt-get update`