Add automatic test (copied from original Github, modified for Gitlab)

.gitlab-ci.yml

+stages:
+  - lint
+  - test
+
+lint:
+  stage: lint
+  image: python:3.13
+  before_script:
+    - apt update && apt install -y curl
+    - curl -LsSf https://astral.sh/uv/install.sh | sh
+    - export PATH="$HOME/.local/bin:$PATH"
+    - uv sync --all-extras --dev
+    - uv tool install pre-commit
+  script:
+    - uvx ruff format --diff
+    - uvx pre-commit run -a
+  only:
+    - master
+    - merge_requests
+
+build_and_test:
+  stage: test
+  image: python:3.10  # Default image (overwritten by matrix)
+  needs: [lint]
+  parallel:
+    matrix:
+      - PYTHON_VERSION: ["3.9", "3.10", "pypy-3.10"]
+  before_script:
+    - apt update && apt install -y curl
+    - curl -LsSf https://astral.sh/uv/install.sh | sh
+    - export PATH="$HOME/.local/bin:$PATH"
+    - uv sync --all-extras --dev
+    - uv tool install mypy
+    - uv tool install ruff
+  script:
+    - uv run pytest -v -s tests/
+  only:
+    - master
+    - merge_requests