Deprecate actions-rs actions

[jku]

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actions-rs actions are unmaintained and archived, we should not be using them. Luckily we weren't really using anything special from them: using rustup(that is part of the GitHub image) and cargo directly should give us the same results

• Use rustup and cargo instead of specific actions
• Use Swatinem/rust-cache to speed up builds

The second part is of course optional. I added it since

• it does speed things up: CI is >1 min faster on wall clock and 4-5 mins faster in total jobs duration
• doing the same thing without a 3rd party action likely leads to annoying debug situations later (rust-cache key calculation seems quite extensive)

Fixes #414