Introduces a relationship system to allow entities to point to other
entities. Includes a `Relationship<TSelf, TTarget>` component and a
`RelationshipIndex` to enable efficient reverse lookups (finding all
sources pointing to a specific target).
The `World.DestroyEntity` method now performs cascading removals:
- Relationships where the entity is the source are removed.
- Relationships where the entity is the target are removed from their
respective source entities.
Also adds MessagePack support to `Entity` and `Relationship`.
Introduces a complete query system for iterating over entities with
specific component combinations, including support for "with" and
"without" filters.
Also adds:
- `ISystem` and `ITickedSystem` interfaces for defining logic.
- `SystemGroup` for managing and running groups of systems.
- `QueryBuilder` for a fluent API to construct queries.
- `QueryExecutor` for high-performance iteration using ref parameters.
- `Tick` and `TickType` to support timed and logical updates.
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)