ci: add style check

Author: AsakuraMizu

.github/workflows/check.yml

@@ -0,0 +1,18 @@
+name: check
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  style:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout machina
+        uses: actions/checkout@v4
+
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Check code formatting
+        run: cargo fmt --all --check