In CI, we use the Swatinem/rust-cache GitHub Action to cache certain build artifacts across runs. However, it seems from the README that we might be using it in a suboptimal way. A few observations:

• Zerocopy has only one dependency, and rust-cache only caches dependencies, not crate artifacts (note that zerocopy-derive has more dependencies - and dependencies that are expensive to compile - so presumably benefits much more than zerocopy)
• We generate a custom cache key which includes:
  • A hash of the Cargo features, but this presumably shouldn't have any effect on dependencies (at least in our case, since none of our Cargo features depend on dependencies' Cargo features)
  • A hash of **/Cargo.lock, but this is documented to be the default behavior anyway

We should:

• Figure out if there's a way to squeeze more benefit out for zerocopy (can we get rust-cache to cache any more artifacts?)
• Don't include Cargo features in the cache
• Don't include a hash of **/Cargo.lock in the cache
• Go back over our use of rust-cache and its README with a fine toothed comb and see what else we're doing suboptimally

cc @Swatinem in case there's anything obvious that jumps out at you!