Session-persistent plot style (avoid repeating aa.plot_settings())

[breimanntools]

Problem

aa.plot_settings(...) must be called before nearly every figure — ≈54 calls across 18 tutorials/protocols, and every cheat-sheet recipe carries one. There is no way to set the publication style once per session.

Goal

Provide an opt-in way to set the plot style once — e.g. an aa.options['plot_settings'] dict applied automatically by plot classes, or an aa.plot_context(...) context manager — so repeated calls are unnecessary; default visuals unchanged when unset.

Requirements

• Add a session-level mechanism in aaanalysis/plotting/ (+ aaanalysis/config.py): options['plot_settings'] applied lazily by plot entry points, or a plot_context manager.
• Default (unset) behavior byte-identical to today (no implicit styling unless opted in).
• Document the one-time setup; update tutorials/cheat sheet to set once.
• numpydoc + Examples.

KPIs / Acceptance

• With the session default set, figures match those from an explicit plot_settings() call (regression test).
• With it unset, output byte-identical to the current default (regression test).
• ≥1 test.

Scope / non-goals

No change to plot_settings defaults; not restyling existing plots.

Dependencies

aaanalysis/config.py is CONFIRM-FIRST. Part of the Simplify API epic #126.

Standards checklist

• config.py CONFIRM-FIRST · numpydoc · regression test.