fix: changed the earliest departure time of agents to 0

[legend5teve]

Module updated: agentevac/simulation/main.py

• In record mode, spawn-event t0 is now ignored at runtime and treated as 0.0.
• Pre-departure agents become eligible immediately; actual release is controlled only by the departure model.
• In replay mode, vehicle release now uses recorded departure events when available.
• Startup now prints the replay departure source:
  • recorded_departure_events
  • or spawn_events_fallback for older logs
• Relevant refs:
  • agentevac/simulation/main.py:1079
  • agentevac/simulation/main.py:1634
  • agentevac/simulation/main.py:1676
  • agentevac/simulation/main.py:1698
  • agentevac/simulation/main.py:1868

Module updated: agentevac/utils/replay.py

• Added replayable departure_release event support.
• Record mode now writes actual departure timing into the replay JSONL.
• Replay mode can now query departure timing per step/vehicle from the recorded run.
• Added:
  • record_departure_release(...)
  • departure_record_for_step(...)
  • has_departure_schedule(...)
• Relevant refs:
  • agentevac/utils/replay.py:249
  • agentevac/utils/replay.py:314
  • agentevac/utils/replay.py:320

Behavior now

1. record mode:

• all agents are eligible from simulation time 0.0
• actual departure time can still vary based on belief/threshold logic

2. replay mode:

• agents are released at the actual recorded departure step/time from the prior run
• if replaying an older log with no recorded departure events, it falls back to SPAWN_EVENTS