MetricComparisons into InformationImbalance + NeighborhoodOverlap; move k*+ID functions into KStar class

[diegodoimo]

Summary

Refactor MetricComparisons class into InformationImbalance and NeighborhoodOverlap, plus relocation of two k* ID-estimation methods to KStar class. Fully backward compatible.

Why

The metric comparisons class is more than 1000 lines long. It contains two conceptually different sets of functions: those used to compute information imbalance and neighborhood overlap, including their helper methods.

What changed

New classes

• InformationImbalance (in dadapy/information_imbalance.py) collects all the 17 imbalance + causality methods (return_inf_imb_*, greedy_feature_selection_*, the causality block).
• NeighborhoodOverlap (in dadapy/neighborhood_overlap.py) containes the neighborhood overlap functions: return_label_overlap, return_data_overlap, and _label_imbalance_helper.
• Both inherit directly from Base. Shared helper _get_nn_indices lifted to dadapy/_utils/metric_comparisons.py as a module-level function.
• Data now inherits from InformationImbalance, NeighborhoodOverlap directly (no through MetricComparisons).

Backward-compatibility

• MetricComparisons shrunk from ~1050 lines to a ~35-line, left for backward compatibility:

  class MetricComparisons(InformationImbalance, NeighborhoodOverlap):
      ...

  Existing code (from dadapy import MetricComparisons, instantiation, method calls) works unchanged.

Symmetric constructor API for the comparison classes

• InformationImbalance(X1, X2).return_information_imbalance()
• NeighborhoodOverlap(X1, X2).return_data_overlap(k=30)
• NeighborhoodOverlap(X, labels=y).return_label_overlap(k=5)
• The existing asymmetric calls via the Data class are unchanged.

Relocation of two k-star ID-estimation methods to KStar class

• return_ids_kstar_gride and return_ids_kstar_binomial moved from Data to KStar, where they conceptually belong; I personally don't understand why those two functions were in Data.
• Data shrank from 243 → 76 lines and is now a pure container.