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.
Initializes the OECS repository with the core foundation, including:
- Entity management with 24-bit IDs and 8-bit versioning
- Sparse set-based component storage
- Entity allocation and recycling logic
- Core World API for entity and component lifecycle
- Project scaffolding for source and unit tests
- Design documentation and architecture decision records (ADRs)
hypercross