Add 4 machine learning algorithms with comprehensive tests

- Decision Tree Pruning: Implements decision tree with reduced error and cost complexity pruning
- Logistic Regression Vectorized: Vectorized implementation with support for binary and multiclass classification
- Naive Bayes with Laplace Smoothing: Handles both discrete and continuous features with Laplace smoothing
- PCA from Scratch: Principal Component Analysis implementation with sklearn comparison

All algorithms include:
- Comprehensive docstrings with examples
- Doctests (145 total tests passing)
- Type hints throughout
- Modern NumPy API usage
- Comparison with scikit-learn implementations
- Ready for TheAlgorithms/Python contribution

Author: omsherikar