Add transform_labels to Transform, Simplex, SumTo1, and ZeroSum #7907

[Mr-Imperium]

Implemented transform_labels method to handle coordinate transformations.

• Base Transform: Identity (returns labels unchanged).
• SimplexTransform: Drops the last label.
• SumTo1: Drops the last label.
• ZeroSumTransform: Implemented logic to drop labels corresponding to zerosum_axes.

Verified via existing test suite and manual verification script.

Description

This PR addresses Issue #7907 by adding a transform_labels method to the base Transform class and overriding it in specific subclasses. This ensures that when transformations (like Simplex) reduce the dimensionality of the data, the associated coordinates/labels are adjusted accordingly.

Changes implemented:

• Base Transform: Added transform_labels which returns labels unchanged (identity).
• SimplexTransform: Overridden to return labels[:-1] (dropping the last label).
• SumTo1: Overridden to return labels[:-1].
• ZeroSumTransform: Overridden to handle zerosum_axes, ensuring the last label is dropped for the specific axes being transformed.

Related Issue

• Closes Add transform_coords method to Transform method to automatically label unconstrained draws #7907
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):