add fmt check

.github/workflows/test.yml

@@ -18,9 +18,22 @@ env:
   POLKADOT_VERSION: polkadot-stable2506-2
 
 jobs:
+  fmt:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+
+      - name: Setup Rust toolchain
+        uses: actions-rust-lang/setup-rust-toolchain@v1
+
+      - name: Cargo fmt
+        run: cargo fmt --all -- --check
+
   cache-polkadot:
     name: Build and cache Polkadot binaries on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
+    needs: [fmt]
     strategy:
       matrix:
         os: [ubuntu-24.04, macos-14]