Add GitHub Actions workflow for linting

Add CI workflow that runs on push to master and on pull requests:
- Runs ruff linter
- Checks code formatting with ruff format

This ensures code quality checks run even for contributors who
haven't installed pre-commit hooks locally.

Author: Mattia Baldari

.github/workflows/lint.yml

@@ -0,0 +1,29 @@
+name: Lint
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+
+jobs:
+  ruff:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.13'
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install ruff
+
+      - name: Run ruff linter
+        run: ruff check .
+
+      - name: Run ruff formatter check
+        run: ruff format --check .