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