ENH: support fixed-time parachute deployment triggers (#437)

[thatrandomasiandev]

Summary

• Adds trigger=("time", t_deploy) so parachutes can deploy at a fixed flight time from launch (motor delay-charge style), addressing ENH: Addition of Time Delay Parachute Deployment #437.
• Flight sets parachute._eval_time before evaluating triggers; no change to the public (p, h, y, sensors, u_dot) triggerfunc signature.
• Burnout-referenced delays are supported by composing with the motor: ("time", motor.burn_out_time + delay). A native ("burnout", delay) trigger is left as a follow-up to avoid coupling Parachute construction to motor state.

Test plan

• Unit tests for ("time", t) True/False at boundary times, ascent-safe behavior, invalid forms, serialization
• Flight._evaluate_parachute_trigger sets _eval_time and fires correctly
• StochasticParachute accepts/rejects time triggers consistently with Parachute
• Integration flight test: deploy within one sampling interval of t_deploy

Fixes #437

[codecov]

Codecov Report

❌ Patch coverage is 92.59259% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.82%. Comparing base (e0ff281) to head (26c35de).
⚠️ Report is 53 commits behind head on develop.

Files with missing lines	Patch %	Lines
rocketpy/stochastic/stochastic_parachute.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1133      +/-   ##
===========================================
+ Coverage    82.18%   82.82%   +0.64%     
===========================================
  Files          122      129       +7     
  Lines        16355    16839     +484     
===========================================
+ Hits         13441    13947     +506     
+ Misses        2914     2892      -22     

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