add type checking to ci

Author: fkromer

.github/workflows/main.yml

@@ -7,7 +7,29 @@ on:
     branches: [main]
 
 jobs:
+  typing:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
+      fail-fast: false
+    defaults:
+      run:
+        shell: bash
+    steps:
+      - name: Check out
+        uses: actions/checkout@v4
+
+      - name: Set up the environment
+        uses: ./.github/actions/setup-python-env
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Run mypy
+        run: uv run mypy .
+
   tests:
+    needs: typing
     runs-on: ubuntu-latest
     strategy:
       matrix: