Ideas for even more CI jobs

[tertsdiepraam]

Some ideas sourced from a Mastodon post:

• zizmor
• cargo-semver-checks
• cargo check on minimal versions
• cargo-machete or cargo-shear or cargo-udeps
• some spell checking, at least for the docs.

In the post there's talk about cargo update --locked --workspace to check whether the lockfile is up to date, but we don't have a lockfile checked in.

Some more ideas for the non-Rust parts of Roto:

• a markdown formatter & linter
• an rst formatter & linter
• a toml formatter (e.g. taplo)

More outlandish ideas:

• Codspeed for performance tracking (requires more benchmarks)
• cargo-tarpaulin for code coverage
• cargo-vet
• More sanitizers? Does e.g. ASAN provide anything that Valgrind doesn't offer?