Deprecate actions-rs actions

[jku]

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

[jku]

If you want to see that the cache works, re-running all CI jobs should work.

[flavio]

Instead of using Swatinem/rust-cache we could use the GitHub's official cache action.

Something like that should work:

      - name: Setup Cache
        uses: actions/cache@6849a6489940f00c2f30c0fb92c6274307ccb58a # v4.1.2
        with:
          path: |
            ~/.cargo/registry
            ~/.cargo/git
            target
          key: ${{ runner.os }}-cargo-clippy-${{ hashFiles('**/Cargo.lock') }}

This is taken from here

[jku]

Sure, I can do that. I wonder if that approach has issues with compiler/toolchain changes though (this is why I chose the action originally)... I suppose if we separate the nightly cache from stable cache these issues might be rare enough.

[flavio]

You're right. Let's stick with your original PR. Can you please rebase it against the main branch?

[jku]

rebased on main, no other changes