fix: add mypy type checking to CI workflow

.gitea/workflows/ci.yml

@@ -31,6 +31,12 @@ jobs:
       - name: Run linting
         run: ruff check src/ tests/
 
+      - name: Install type checker
+        run: pip install mypy
+
+      - name: Run type checking
+        run: mypy src/ tests/
+
   build:
     needs: test
     runs-on: ubuntu-latest