feat: Implement 3D flight animation methods using Vedo (Issue #523)

[Copilot]

Adds animate_trajectory and animate_rotate to the Flight plots layer, enabling interactive 3D visualization of simulated rocket trajectory and attitude via the optional vedo dependency. Resolves merge conflicts and addresses all reviewer comments from PR #909.

Pull request type

• Code changes (bugfix, features)
• Code maintenance (refactoring, formatting, tests)
• ReadMe, Docs and GitHub updates

Checklist

• Tests for the changes have been added (if needed)
• Docs have been reviewed and added / updated
• Lint (black rocketpy/ tests/) has passed locally
• All tests (pytest tests -m slow --runslow) have passed locally
• CHANGELOG.md has been updated (if relevant)

Current behavior

No built-in 3D animation of rocket trajectory or attitude exists in the Flight class.

New behavior

Two animation methods accessible via flight.plots.*, backed by vedo as an opt-in dependency (pip install rocketpy[animation]):

# 6-DOF trajectory + attitude
flight.plots.animate_trajectory(start=0.0, stop=20.0, time_step=0.05)

# Rotation-only (attitude held at start position)
flight.plots.animate_rotate(file_name="rocket.stl", start=0.0, stop=20.0, time_step=0.05)

Key implementation details:

• Methods live in rocketpy/plots/flight_plots.py (not simulation/flight.py) per project convention
• Built-in fallback STL model at rocketpy/plots/assets/default_rocket.stl; bundled via [tool.setuptools.package-data]
• Correct quaternion → axis-angle conversion: angle = 2·arccos(q0), with np.clip guard and zero-division protection for near-identity quaternions
• World bounding box enforces a 10 m minimum dimension to remain visible for short-range trajectories
• _validate_animation_inputs() raises ValueError for invalid [start, stop] or non-positive time_step, and FileNotFoundError for missing STL paths
• ImportError with install hint raised via existing import_optional_dependency("vedo") if vedo is absent
• vedo>=2024.5.1 added as rocketpy[animation] optional group; included in rocketpy[all]

Tests added (tests/unit/test_plots.py):

• Happy-path execution with fully mocked vedo
• ImportError when vedo is absent
• ValueError for reversed/out-of-range time interval and time_step ≤ 0
• FileNotFoundError for missing STL (explicit path and missing default)

Breaking change

• No

Original prompt

Can I have your help on PR 909? Merging conflicts, solving differente comments, and testing the feature

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