ci: consolidate rust + protoc install across workflows (#23700)

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/pr-test.yml

@@ -725,11 +725,16 @@ jobs:
 
       # Needed by setuptools-rust to build the bundled native gRPC extension
       # (rust/sglang-grpc) when installing the main `sglang` wheel from source.
-      - name: Install protoc
-        run: sudo bash scripts/ci/utils/install_protoc.sh
+      - name: Install protoc + Rust toolchain
+        timeout-minutes: 10
+        run: bash scripts/ci/utils/install_rust_protoc.sh
 
-      - name: Install Rust toolchain
-        run: bash scripts/ci/utils/install_rustup.sh
+      - name: Rust cache (sglang-grpc)
+        uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: rust/sglang-grpc
+          shared-key: "sglang-grpc-cpu"
+          save-if: ${{ matrix.partition == 0 }}
 
       # uv pip targets a venv by default; setup-python has no venv — install into that interpreter (see UV_SYSTEM_PYTHON in https://docs.astral.sh/uv/guides/integration/github/)
       - name: Install dependencies