Rust Warm Cache Action

A GitHub Action that keeps a warm cache for large Rust projects and never handout a cold cache for any of the CI jobs.

This should be akin to local developments where you checkout branches to work on while the target directory persists.

This action differentiates Swatinem/rust-cache by:

this caches workspace crates because they still take a significant amount of time to build. Swatinem/rust-cache does not cache workspace crates.
controls the size of the cache so it does not reach a few gigabytes if the builds are frequent

This action builds upon actions/cache@v3 so you don't need to learn about the complicated caching strategies.

Future work

Figure out a way to work with sccache, as sccache action is not ideal for GitHub actions due to:

429 rate limit when run in parallel
if Swatinem/rust-cache is not installed, cargo will still have to download the crates, countering the performance improvement
too many cache objects (1000+), this may "push out" all the other larger caches because of the 10GB site limit.