hypercross
8557fc864d
Introduces a mechanism to store and access singleton components on a reserved entity. The singleton entity is automatically excluded from all standard queries to prevent it from being processed like regular entities. - Added `SetSingleton`, `GetSingleton`, `HasSingleton`, and `RemoveSingleton` to `World`. - Added `RegisterSingleton` to `EntityAllocator` to support the reserved entity. - Updated `QueryExecutor` to skip the singleton entity during iteration. - Added unit tests for singleton functionality.