Renames `Layer<D>` to `TypedLayer<D>` to establish a distinct typed abstraction. Introduces a new heterogeneous `Layer` enum that unifies count and presence storage with runtime dispatch, delegating operations to the underlying typed variants. Updates cache, index, and phylo consumers to align with the renamed type and new extension traits, preserving full test suite stability while preparing the foundation for multi-partition caching.
Eric Coissac
1c54e60c9a