[max-models]

Part of making the formatting setup the same in all max-models repos.

• .pre-commit-config.yaml is now the shared one: pre-commit-hooks v6.0.0 (with check-toml), nbstripout 0.9.1, ssort 0.17.0, ruff-check --fix and ruff-format at v0.17.3.
• ruff is the only formatter and sorts imports (its I rules); CI and make lint also check statement order with ssort.
• The rest of the diff is pre-commit run --all-files with the new hooks.
• black and isort are dropped from the dev extra, [tool.black]/[tool.isort] and CI; the ruff job checks the whole repo and is no longer continue-on-error.
• ruff lints with an explicit rule set (E4, E7, E9, F, I), since its default set grows between releases.
• Fix: the module-level plot_matplotlib passed fontsize=self._fontsize without a self, a NameError for any node with content; the text now uses the font size the canvas sets in matplotlib's rcParams.
• Removed an exact duplicate Canvas.legend definition.
• README.qmd carries the same code formatting as the rendered README.md.