Add ccache action for caching C++ build artifacts

.github/workflows/cpp-rllm.yml

@@ -18,6 +18,7 @@ jobs:
     - uses: actions/checkout@v3
       with:
         submodules: true
+    - uses: hendrikmuhs/[email protected]
     - uses: Swatinem/rust-cache@v2
       with:
         cache-on-failure: true