Add preprocessing and PCA-based hyperspectral classification example

[Slash-495]

This PR adds a simple preprocessing and classification example for hyperspectral data using Spectral Python.

Changes include:

• Added a demonstration script showing normalization, PCA-based dimensionality reduction, and classical ML classification.
• Included basic visualization of RGB composites for hyperspectral images.
• Documented the example in the README.

The script uses synthetic hyperspectral-like data by default to validate the pipeline and can be extended to real datasets.