chore: Update GitHub Actions CI

[striezel]

The following updates are performed:

• update actions/checkout to v4
• replace unmaintained actions-rs/toolchain by dtolnay/rust-toolchain
• replace unmaintained actions-rs/cargo by direct invocation of cargo where possible

Still using the outdated / unmaintained actions will generate several warnings in CI runs, for example in https://github.com/spicylobstergames/astratomic/actions/runs/7363212173:

The following actions uses node12 which is deprecated and will be forced to run on node16: actions-rs/toolchain@v1, actions-rs/cargo@v1, actions/upload-artifact@v2. For more info: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

The PR will get rid of some of those warnings.

[Zac8668]

Thanks! I'm not good with Github Actions. Gonna take advantage of this to push a bug fix release I was meaning to push earlier