Emitting game events with context

Use LevelRef::game_event(host, event, at, context) to emit a vanilla game event at an explicit position. For example, event can be "minecraft:block_change" and at is an [f64; 3] position. This is a server operation; vibration listeners such as sculk sensors and wardens hear the event through the normal game path.

GameEventContext mirrors vanilla's GameEvent.Context:

• source_entity: Option<EntityRef> identifies the responsible entity. Its current spectator, sneaking, vibration-dampening and other listener facts are captured when the event is emitted.
• affected_state: Option<BlockState> identifies the state affected by the action, not necessarily the state currently at the position. Wool, for example, dampens the vibration when supplied as the affected state.

Use GameEventContext::default() when neither field applies. Both fields cross the same Wire boundary on native and wasm. An unknown event, invalid position, stale or foreign source, invalid state or inactive level returns false without emitting an event. A source must belong to the level in place.

EntityRef::game_event(host, event) is the convenience operation for an event at the entity's position with that entity as source and no affected state. It calls the same level operation; use the level form when the position or state differs.