Add code formatting and linting to CI

.github/workflows/tests.yml

@@ -3,12 +3,18 @@ name: Tests
 on:
   push:
     branches: main
+  pull_request:
+    branches: main
 
 jobs:
   build:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
       uses: actions/checkout@v3
+    - name: Check code formatting is consistent
+      run: cargo fmt --check
+    - name: Lint code
+      run: cargo clippy
     - name: Run all tests
       run: cargo test