ci: Cache Rust compilation and cargo dependencies

I noticed that Wasmtime uses almost no cache for its GitHub Actions workflows. Let's see how well adding a cache for `target` plus various `cargo` dirs works.

Author: tschneidereit

.github/actions/install-rust/action.yml

@@ -74,3 +74,15 @@ runs:
     - name: Install the WASI target
       shell: bash
       run: rustup target add wasm32-wasip1 wasm32-unknown-unknown
+
+    - name: Set up cargo cache
+      uses: actions/cache@v4
+      with:
+        path: |
+          ~/.cargo/bin/
+          ~/.cargo/registry/index/
+          ~/.cargo/registry/cache/
+          ~/.cargo/git/db/
+          target/
+        key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+        restore-keys: ${{ runner.os }}-cargo-