Add documentation to Cache and fix a possible bug

[connec]

• e8ed35b8 docs(cache): Populate empty doc comments

• a67164c7 refactor(cache): Avoid suppressing lints

• b5dab42c fix(cache): Prevent exposing expired values from Cache::set

  Cache::set was not testing the removed item's expiry, meaning expired values could be returned.

• 93de8c87 ci: Install cargo-udeps without --locked

  This works around a compilation issue caused by https://github.com/rust-lang/rust/issues/85574. A more permanent fix may come in future.

• 37fc9daf chore: Remove unused dashmap dependency

  This has been unused since #2556.

[connec]

Had to fix a couple of actions issues @dirvine, but it's green across the board now!