Add t-SNE algorithm for dimensionality reduction (#13432)

[Nikita-Kedari]

Description

This PR adds a full educational implementation of t-SNE in Python.
It includes:

• High-dimensional similarity computation (P matrix)
• Low-dimensional embedding using Student-t distribution (Q matrix)
• Gradient descent with momentum to minimize KL divergence
• Docstrings, type hints, and doctests for educational purposes
• Updated DIRECTORY.md to include t-SNE

How to test

python machine_learning/tsne.py

[algorithms-keeper]

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