Exposes views on the HDBSCAN cluster exemplars

[Craigacp]

Description

Adds a get method for cluster exemplars in HDBSCAN which returns copies of the exemplars (as the vector is mutable), along with a method that returns the exemplar in terms of feature names.

Motivation

Fixes #217.

[Craigacp]

@geoffreydstewart would you mind looking over this?

[geoffreydstewart]

These changes look good. I'm not sure if it's worth adding some minimal test coverage for the new getClusters method. The logic looks quite safe, but it could be instructive for the community. Additionally, there is an existing test deserializeHdbscanModelV42Test where we might consider asserting that calling the getMaxDistToEdge method on a ClusterExemplar from a v4.2 model returns Double.NEGATIVE_INFINITY.

[Craigacp]

These changes look good. I'm not sure if it's worth adding some minimal test coverage for the new getClusters method. The logic looks quite safe, but it could be instructive for the community. Additionally, there is an existing test deserializeHdbscanModelV42Test where we might consider asserting that calling the getMaxDistToEdge method on a ClusterExemplar from a v4.2 model returns Double.NEGATIVE_INFINITY.

I've expanded the tests to cover those points.

[geoffreydstewart]

The added coverage looks great.

[JackSullivan]

Looks good to me