ENH: add Flight post-step callback across all phases (#758)

[thatrandomasiandev]

Pull request type

• Code changes (bug fix, features)

Checklist

• Tests for the changes have been added (if needed)
• Docs have been reviewed and added / updated
• Lint (ruff / make lint focused files) has passed locally
• All tests (pytest tests -m slow --runslow) have passed locally
• CHANGELOG.md — no action needed; an LLM workflow auto-updates it after merge

Current behavior

Discrete/continuous controllers are not a full-lifecycle observer: air-brake examples often terminate at apogee, and parachute phases are not meant to keep feeding actuator controllers. Users simulating ground-station / radio update code had no first-class hook that keeps running through descent.

Fixes #758

New behavior

Flight(..., post_step_callback=None) accepts an optional callable invoked once after every successful ODE solver step for the entire simulation, including parachute phases. Signature matches phase/node callbacks: callback(flight). Use flight.t and flight.y_sol for the current time and state.

Breaking change

• No

Additional information

• Focused unit tests assert the callback fires both before and after apogee on calisto_robust, and that non-callables raise TypeError.
• Full slow suite not run in this contribution pass.