Add cluster export and t-SNE caching

[FBartos]

Adds export support for clustering results (predicted cluster, soft memberships, and t-SNE coordinates) with new helper functions (.mlClusteringExportResultsToData, AddCluster/SoftMemberships/TSNE helpers and caching).
Computes soft memberships for fuzzy-cmeans, model-based and RF (from proximity) and normalizes them. Moves t-SNE to reusable cached routine handling duplicate rows.
Fixes randomForest predict calls to pass only predictor columns (classification/regression/DALEX explain).

[github-actions]

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[koenderks]

Couple questions without looking at the code yet:

1. We already export the predicted cluster, right?

2. What is the use case for exporting the T-sne coordinates? I'm struggling to see one because they don't mean anything and are not fixed for a dataset. Weighing that with potential UI clutter makes me thing whether we really need it.