ENH: time based triggering of parachute

[aZira371]

Pull request type

• Code changes (bugfix, features)
• Code maintenance (refactoring, formatting, tests)

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

RocketPy cannot simulate rockets with motor delay charges (fixed-time deployment) like model rocket motors or high-power motors without avionics. Users must resort to workarounds or cannot accurately simulate kits like Loc-IV powered by Aerotech motors with delay elements. #437

New behavior

Parachute triggers now accept time-based string formats:

• "launch + X" - deploys X seconds after t=0
• "burnout + X" - deploys X seconds after motor burnout

Implementation:

• Extended Parachute.__evaluate_trigger_function() to parse time-based triggers
• Added t (current time) and rocket (motor access) parameters to trigger function signature
• Maintained backward compatibility via parameter count detection (existing pattern)
• Updated all four call sites in Flight class to pass additional parameters (two original + two new)

Example usage:

# Model rocket with 3-second motor delay (like Estes C6-3)
rocket.add_parachute(
    name="Main",
    cd_s=10.0,
    trigger="burnout + 3",
    sampling_rate=100,
    lag=1.5,
)

# Simple timer deployment 5 seconds after launch
rocket.add_parachute(
    name="Drogue",
    cd_s=1.0,
    trigger="launch + 5",
    sampling_rate=100,
    lag=0.5,
)

Testing:

• 11 unit tests covering parsing, functionality, edge cases, backward compatibility
• 4 integration tests with full flight simulations with time-based triggers

Breaking change

• Yes
• No

Additional information

Existing trigger types (callable, float altitude, "apogee") remain unchanged. The trigger function signature extension uses optional parameters with defaults, ensuring zero-impact to existing code

[codecov]

Codecov Report

❌ Patch coverage is 96.96970% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.04%. Comparing base (9cf3dd4) to head (6814de7).
⚠️ Report is 27 commits behind head on develop.

Files with missing lines	Patch %	Lines
rocketpy/rocket/parachute.py	94.28%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #923      +/-   ##
===========================================
+ Coverage    80.27%   81.04%   +0.76%     
===========================================
  Files          104      107       +3     
  Lines        12769    13893    +1124     
===========================================
+ Hits         10250    11259    +1009     
- Misses        2519     2634     +115     

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