Move away from `actions-rs`

[tgross35]

actions-rs is archived and will stop working at some point when GitHub switches to node 16 for runners.

A better option would be to switch to dtolany/rust-toolchain, or just use the preinstalled rustup.

A lot of tools use https://github.com/Swatinem/rust-cache for cache now, this could replace that portion of actions-rs.

[emilio]

I'd be happy with either of those options. @pvdrz / Ferrous have done a lot of work on automation, any preference?

[tshepang]

I would go for dtolnay/rust-toolchain, and have not used rust-cache