Clear oceanic clearance cache on flight plan updates to fix track display

[MrAdder]

Potentially Fixes #586

Currently unable to test this

Summary of Changes

Your changes fix an issue where assumed aircraft would show incorrect oceanic track information. The modifications improve the oceanic clearance caching mechanism by:

Files Modified:

1. src/plugin/oceanic/OceanicEventHandler.h - Header file

   • Added include for FlightPlanEventHandlerInterface
   • Made OceanicEventHandler inherit from FlightPlanEventHandlerInterface (in addition to existing base classes)
   • Added three new method declarations for flight plan event handling

2. src/plugin/oceanic/OceanicEventHandler.cpp - Implementation file

   • Improved code formatting/indentation in the UpdateOceanicClearances() method
   • Implemented FlightPlanEvent() - Clears cached clearance data when a flight plan is updated (including when an aircraft is assumed)
   • Implemented FlightPlanDisconnectEvent() - Removes clearance from cache when a flight plan disconnects
   • Implemented ControllerFlightPlanDataEvent() - Empty handler for controller flight plan data events

Technical Details:

The changes use thread-safe operations (std::lock_guard with clearanceMapMutex) to ensure cache consistency when clearing or removing oceanic clearances during flight plan lifecycle events.

Issue Fixed:

When aircraft are assumed or their flight plans update, the oceanic clearance cache is now properly invalidated, ensuring fresh data is displayed on the next timer trigger rather than showing stale cached information.