feat(ci): add rust-cache to accelerate tests

Adds `Swatinem/rust-cache@v2` to the CI workflow to cache Cargo dependencies
and build artifacts. This will significantly reduce build times for subsequent
runs by avoiding redundant compilation of dependencies.

Co-authored-by: 404Setup <[email protected]>

Author: google-labs-jules[bot]

.github/workflows/ci.yml

@@ -17,6 +17,8 @@ jobs:
       - uses: actions/checkout@v4
       - name: Set up Rust
         uses: dtolnay/rust-toolchain@nightly
+      - name: Rust Cache
+        uses: Swatinem/rust-cache@v2
       - name: Build
         run: cargo build --verbose
       - name: Run tests