fix(sirens): track active rotators per vehicle instance to prevent dangling pointer crashes

[CanerKaraca23]

Summary

Fixes a dangling pointer crash in the sirens system when multiple instances of the same emergency vehicle model exist simultaneously or when an instance is despawned.

Details

• Previously, Sirens::modelRotators stored active rotator dummy pointers in a static model-indexed map (std::map<int, std::vector<VehicleDummy *>> modelRotators).
• When multiple vehicles shared the same model index or a vehicle instance was deleted while another was running, rotator dummy pointers in modelRotators would be overwritten or refer to freed vehicle memory, causing access violation crashes during ResetAngle().
• Moves ActiveRotators tracking into per-vehicle extended data (VehicleSirensData::ActiveRotators), guaranteeing safe per-instance lifecycle management without cross-vehicle interference.