chore(CI): Tighten and modernize code style checks
chore(CI): Tighten and modernize code style checks

- Tests and feature-dependent sections of code will now be
  checked by clippy, and any warnings will lead to a failing check.
- The `cargo check` and `cargo clippy` invocations no longer use the
  deprecated `--all` flag, which has been replaced by `--workspace`.
- Use `--all-targets` for `cargo check` instead of enabling the
  targets individually.

cobalt-org/cobalt.rs,cobalt-org/cobalt.rs,cobalt-org/cobalt.rs,cobalt-org/cobalt.rs