CI: Add code format checker.

.github/workflows/pr-code-format.yaml

@@ -0,0 +1,25 @@
+name: "Check code formatting"
+
+on:
+  pull_request:
+
+jobs:
+  checker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 1
+      - name: Prepare
+        run: |
+          wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
+          sudo add-apt-repository -y 'deb http://apt.llvm.org/jammy/ llvm-toolchain-jammy main'
+          sudo apt install clang-format
+      - name: Format
+        run: |
+          find src -iname "*.[h,c]" -exec clang-format -i {} \;
+      - name: Check
+        run: |
+          git status
+          git diff --quiet