Add gradual rasterizer for silo team's review.

[ray-anirudh]

This notebook builds on the original work of pyGr, a Python port and extension of the Gradual Rasterization Tool (gr), as described in: Molloy, J., Moeckel, R. Automated design of gradual zone systems. Open geospatial data, softw. stand. 2, 19 (2017). https://doi.org/10.1186/s40965-017-0032-5

Purpose of Contribution
The notebook provides:

1. A structured implementation of the zoning algorithm using population and employment rasters.
2. Validation and visualization of zone outputs for a custom regional use case.
3. Modular code blocks for preprocessing, configuration parsing, and iterative zone generation.

Key Features

1. Compatible with pyGr’s existing configuration structure.
2. Designed to support iterative zone refinement and municipal boundary alignment.
3. Includes comments and markdown cells for clarity and reproducibility.

Notes
I hope this contribution is useful for further development and documentation of pyGr. Feedback and suggestions are welcome!