ci: cache build artifacts

.github/workflows/ci.yml

@@ -17,10 +17,18 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@master
+      - name: toolchain
+        uses: dtolnay/rust-toolchain@stable
         with:
           toolchain: nightly
           components: rustfmt, clippy
+      - name: cache
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}-rustc-${{ steps.toolchain.outputs.cachekey }}
       - name: cargo test
         run: cargo test --lib --bins --tests
       - name: cargo fmt