Add wavelet-based image denoising example

[beauagainagainagainagainagain]

Summary

• add a wavelet-based denoising example with helper utilities for normalization and conversion
• demonstrate PSNR improvements using soft-thresholded wavelet reconstruction
• declare PyWavelets and scikit-image dependencies required for the example

Testing

• python -m compileall digital_image_processing/wavelet_denoising.py

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https://chatgpt.com/codex/tasks/task_e_68ca77ee22448320a7c39301327f18f7