New scene trigger executor system

Background

Scene trigger executors do not have proper editor tools, and use strings for identifying classes, functions and fields. They are therefore easy to break, and given that there are no editor tools, often fail silently and kaskade errors.

From https://openhellion.github.io/documentation/level-design:

Triggers are objects that execute an action when triggered. Every trigger has a trigger event. This is an event that causes the trigger to trigger the action it is set to do.
Functionally, triggers are a kind of “sensor” in the game, and is the main way players affect the world. Fulfillement of many quests are handled by triggers, while other uses are buttons for opening and closing doors.

Proposal

Create a new system to replace scene triggers that makes better use of native unity features, has input validation and has compile-time and editor checks.

System should work in parallell with the old system with gradual migration when needed.

Start with the existing scene trigger system and the level-design documentation linked in the issue to understand current trigger behavior. Map how triggers identify classes, functions, and fields, then define the replacement boundaries and migration path. Done means a Unity-native system can coexist with the old system while providing input validation and compile-time and editor checks.