Add CI: ruff lint and pytest on Python 3.10-3.13

.github/workflows/ci.yml

@@ -0,0 +1,65 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+          cache: pip
+          cache-dependency-path: pyproject.toml
+
+      - name: Install
+        run: python -m pip install -e ".[dev]"
+
+      # `ruff format --check` is not enforced yet: the existing sources are not
+      # format-clean, and reformatting them belongs in its own PR.
+      - name: Ruff
+        run: ruff check .
+
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        python-version: ["3.10", "3.11", "3.12", "3.13"]
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+          cache: pip
+          cache-dependency-path: pyproject.toml
+
+      - name: Install
+        run: python -m pip install -e ".[dev]"
+
+      # pytest exits 5 when it collects no tests. main has no tests yet, so
+      # treat 5 as success until the first test file lands; every other
+      # non-zero code still fails the job.
+      - name: Pytest
+        run: |
+          set +e
+          pytest -q
+          code=$?
+          if [ "$code" -eq 5 ]; then
+            echo "::notice::pytest collected no tests (exit 5); treating as success."
+            exit 0
+          fi
+          exit "$code"