HDBSCAN Adapter

The adapter must be the only module that directly imports HDBSCAN private APIs. CoreSG and CoreSGClusterer should not import HDBSCAN private modules directly.

The intended dependency direction is:

CoreSG -> core_sg.hdbscan_adapter -> HDBSCAN internals

Responsibilities

The adapter handles reference MST construction, single linkage conversion, tree-to-label conversion, tree wrapper creation, and compatibility filtering for private _tree_to_labels(...) keyword arguments.

This boundary localizes version risk. If HDBSCAN changes a private signature, core_sg/hdbscan_adapter.py should be the first place to update.