Drop support for Python 3.9

[aclerc]

I saw an error XIO: fatal IO error 0 (Success) on X server "localhost:10.0" when trying to run wind-up on a server overnight. Typical useage of wind-up is fine with Agg as mpl backend so make that happen by default.

During this PR I ran uv lock -U and found the latest matplotlib has dropped support for Python 3.9. 3.9 became EOL in late 2025 so makes sense to drop it now. I looked in to supporting 3.14 but that deserves another PR.

[Copilot]

Pull request overview

This PR updates wind-up to drop Python 3.9 support (aligning with upstream dependency support) and makes matplotlib default to a headless-safe backend to avoid X-server related failures during unattended runs.

Changes:

• Drop Python 3.9 support across packaging/tooling and migrate strict_zip backport usage to zip(..., strict=True).
• Default matplotlib backend to Agg on import wind_up unless MPLBACKEND is explicitly set, and add tests for this behavior.
• Minor cleanups: plotting arg style tweaks, small typing improvements, and README updates (methodology link + backend note).

Reviewed changes

Copilot reviewed 23 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
wind_up/scada_funcs.py	Replace strict_zip with built-in zip(..., strict=True) after dropping Py3.9.
wind_up/pp_analysis.py	Make bootstrap override handling explicit (is not None).
wind_up/plots/scada_funcs_plots.py	Replace strict_zip with zip(..., strict=True).
wind_up/plots/pp_analysis_plots.py	Minor matplotlib call style tweak (ylim tuple).
wind_up/plots/northing_plots.py	Minor matplotlib call style tweak (xlim tuple).
wind_up/plots/data_coverage_plots.py	Minor matplotlib call style tweaks (xlims tuple, ylim tuple).
wind_up/plots/combine_results_plots.py	Replace strict_zip with zip(..., strict=True) and enforce strictness.
wind_up/optimize_northing.py	Replace strict_zip with zip(..., strict=True).
wind_up/northing.py	Use circ_median directly as a groupby aggfunc.
wind_up/models.py	Replace strict_zip with zip(..., strict=True) in YAML config construction.
wind_up/backporting.py	Remove backport module now that Py3.10+ is required.
wind_up/init.py	Set default matplotlib backend to Agg unless MPLBACKEND is set.
tests/test_smart_data.py	Update tests to use zip(..., strict=True).
tests/test_rolling_circ_median.py	Small refactor: pass function directly into rolling.apply.
tests/test_rolling_circ_mean.py	Minor lambda cleanup in expected-series computation.
tests/test_backporting.py	Remove tests for backported strict_zip (module removed).
tests/test_backend.py	Add regression tests verifying backend defaulting + env override behavior.
tests/pp_analysis/test_cook_pp.py	Use zip(..., strict=True) in test data construction.
README.md	Document Py3.10–3.13 support, add methodology link + backend note.
pyproject.toml	Bump version, require Py3.10+, adjust tooling config and dependency constraints.
examples/smarteole_utils.py	Modernize typing to Py3.10 union (`
examples/kelmarsh_kaggle.py	Improve typing annotation for automl_settings.
.github/workflows/lint-and-test.yaml	Update CI matrix to test Python 3.10 and 3.13.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.