Introduce a "cargo fmt" github action gate

This should prevent non-fmt code from hitting the master branch.

.github/workflows/rust-checks.yml

@@ -0,0 +1,26 @@
+name: Rust Checks
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  fmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt
+
+      - name: Check formatting
+        run: cargo fmt --all -- --check