Repeated Multi-k Workloads

The intended workload is:

clusterer = CoreSGClusterer(k_max=50)

for k in range(50, 1, -1):
    clusterer.fit(X, k=k)

For CoreSGClusterer, repeated calls to fit(X, k=...) after the first call reuse core_sg_ and should be interpreted as extraction cost, not a full rebuild.

This is the workload where Core-SG is expected to differ most from running HDBSCAN independently for each k.