CI: add GitHub actions caching for Rust (#754)

Author: guybedford

.github/workflows/pullrequest.yml

@@ -17,6 +17,17 @@ jobs:
           components: clippy, rustfmt
           targets: wasm32-unknown-unknown
 
+      - name: Cache Rust dependencies
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
       - name: Check Formatting
         run: cargo fmt --all -- --check
 
@@ -37,6 +48,17 @@ jobs:
         with:
           targets: wasm32-unknown-unknown
 
+      - name: Cache Rust dependencies
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
       - name: Check for errors
         run: cargo check