Enhance documentation for machine learning algorithms

[Shekhar0109]

Describe your change:

Enhanced documentation for multiple machine learning algorithms:

• decision_tree.py

  • Added detailed module-level docstring with:
    • Overview
    • Features
    • Educational value
    • Use cases
    • Audience
    • Dependencies
    • Notes

• linear_regression.py

  • Expanded docstring to include:
    • Purpose
    • Audience
    • Dependencies
    • Notes

• logistic_regression.py

  • Improved top-level docstring with:
    • Audience
    • Dependencies
    • Notes
    • References

These changes make the algorithms easier to understand for students, beginners, and contributors learning machine learning concepts.

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Checklist:

• Documentation change (no logic modifications)
• Each file now includes Audience, Dependencies, and Notes
• Docstrings follow Python conventions and provide references
• No functional code was altered; only comments/docstrings were enhanced

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Issue Reference:

Closes #13029