Summary

• Align README, Read the Docs, and docs CI SciPy lower-bound references with pyproject.toml's scipy>=1.10 runtime requirement.
• Leave normal test workflows that install latest scipy unchanged.
• Wrap DID_+, DID_-, and DID_M as inline code in the dCDH tutorial so the Sphinx -W docs build does not treat the underscores as unresolved reference targets.

Closes #571.

Methodology references (required if estimator / math changes)

• Method name(s): N/A - documentation and docs-CI dependency metadata only
• Paper / source link(s): N/A
• Any intentional deviations from the source (and why): N/A

Validation

• Tests added/updated: N/A - no runtime behaviour change
• Backtest / simulation / notebook evidence (if applicable): N/A
• Commands run:
  • rg -n 'scipy\\s*>?=\\s*1\\.7|scipy>=1\\.7' README.md .readthedocs.yaml .github docs pyproject.toml returned no matches
  • Python 3.9 docs dependency install smoke passed in a temporary venv; resolved scipy 1.13.1, sphinx 7.4.7, pydata-sphinx-theme 0.16.1, nbsphinx 0.9.8
  • PYTHONPATH=. DIFF_DIFF_BACKEND=python pytest tests/test_doc_snippets.py tests/test_doc_deps_integrity.py -q passed: 265 passed, 4 skipped
  • make -C docs html SPHINXOPTS=\"-W\" passed

Security / privacy

• Confirm no secrets/PII in this PR: Confirmed