Add ecommerce carton sample data

[Packrift]

Summary

Adds a small ecommerce-carton input instance and a parser test for it. The sample follows the existing text input format and gives the demo one more concrete case with multiple item quantities and a two-bin cap.

Notes

• input/sample_data_ecommerce_cartons.txt uses 24x10x8 carton dimensions from a static public ecommerce packaging corpus sample.
• The fixture stays intentionally small so it can be used for parser/model setup checks without requiring a cloud solver run.
• Attribution/source: https://github.com/Packrift/packaging-optimization-benchmark-corpus/blob/main/examples/ortools-carton-selection/sample_cartons.csv

Testing

• git diff --check
• Parsed input/sample_data_ecommerce_cartons.txt locally with a small standalone Python check matching the expected rows.
• Full test suite not run locally: this environment does not have the repository's Python dependencies installed (dimod is missing).