Extend image-processing functionality (histogram & thresholding tools)

[uxabix]

Description

Add several new image-processing features commonly used in educational and real-world environments.
The goal is to expand the toolkit while maintaining the structure and style of existing filters.

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New functionality to add

1. Histogram-based operations

• Histogram stretching (contrast stretching)
• Histogram equalization
• Optional: per-channel vs grayscale implementations

2. Binarization / Thresholding

• Manual thresholding (user-defined cutoff)
• Percentage thresholding (percentile-based)
• Otsu thresholding (automatic)

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Requirements

Each new operation must:

• support both grayscale and RGB (using the existing decorator),
• avoid clipping artifacts,
• return a valid uint8 image,
• be integrated into the examples generation script (examples.py),
• include tests if applicable.