Fix mypy errors, add notebook CI, clean up TODO #1

	name: Tutorial Notebooks

	on:
	push:
	branches: [main]
	paths:
	- 'docs/tutorials/**'
	- 'diff_diff/**'
	- 'pyproject.toml'
	- '.github/workflows/notebooks.yml'
	pull_request:
	branches: [main]
	paths:
	- 'docs/tutorials/**'
	- 'diff_diff/**'
	- 'pyproject.toml'
	- '.github/workflows/notebooks.yml'
	schedule:
	# Weekly Sunday 6am UTC — catches external breakage (dataset URLs, etc.)
	- cron: '0 6 * * 0'

	jobs:
	execute-notebooks:
	name: Execute tutorial notebooks
	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v4

	- name: Set up Python
	uses: actions/setup-python@v5
	with:
	python-version: '3.11'

	- name: Install dependencies
	run: \|
	pip install numpy pandas scipy matplotlib nbmake pytest

	- name: Execute notebooks
	run: \|
	DIFF_DIFF_BACKEND=python PYTHONPATH=. pytest --nbmake docs/tutorials/ \
	--nbmake-timeout=300 \
	-v \
	--tb=short

	- name: Upload failed notebook outputs
	if: failure()
	uses: actions/upload-artifact@v4
	with:
	name: failed-notebook-outputs
	path: docs/tutorials/*.ipynb
	retention-days: 7

Provide feedback