Cache build artifacts in CI

Our CI is somewhat slow, mostly owing to the long time it takes to build
the slew of dependencies we have.
To mitigate this problem, cache build artifacts so that they can be
reused between CI runs.

.github/workflows/test.yml

@@ -39,6 +39,9 @@ jobs:
     steps:
     - uses: actions/checkout@v4
     - uses: dtolnay/rust-toolchain@stable
+    - uses: Swatinem/rust-cache@v2
+      with:
+        key: ${{ matrix.profile }}-${{ matrix.args }}
     - name: Build ${{ matrix.profile }}
       run: cargo build --profile=${{ matrix.profile }} --all-targets ${{ matrix.args }}
   build-minimum:
@@ -55,6 +58,7 @@ jobs:
           # Please adjust README and rust-version field in Cargo.toml files when
           # bumping version.
           toolchain: 1.63.0
+      - uses: Swatinem/rust-cache@v2
       - name: Build
         run: cargo build --features=vendored-openssl --locked
   test:
@@ -64,6 +68,7 @@ jobs:
     - uses: actions/checkout@v4
     - name: Install cargo-llvm-cov
       uses: taiki-e/install-action@cargo-llvm-cov
+    - uses: Swatinem/rust-cache@v2
     - name: Test and gather coverage
       run: cargo llvm-cov --lcov --output-path lcov.info --ignore-filename-regex=src/api/v2/de.rs
       env:
@@ -81,6 +86,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
       - run: cargo clippy --no-deps --all-targets --all-features -- -A unknown_lints -D warnings
   rustfmt:
     name: Check code formatting
@@ -99,6 +105,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
       - run: |
           cargo doc --no-deps
           # Explicitly run doc tests as cargo-llvm-cov currently does not.