Add new compression format

[yemeen]

Pull Request

Summary

adds a way to compress ECTResult

Description

adds option to save ECTResult as an array of jump values instead. removes redundant calculation of +1 for each vertex.

Motivation and Context

saves 50% more space.

ECT storage comparison (compressed .npz)
nodes=3000, edges=1200, dirs=180, thresh=180
dense:  34.27 KB (35096 bytes)
sparse: 22.74 KB (23290 bytes)
ratio dense/sparse: 1.51x

How has this been tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• [ x ] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvement

Checklist

• [ x ] My code follows the code style of this project. (make clean)
• [ x ] I have incremented the version number in the pyproject.toml file (if applicable).
• [ x ] I have added tests to cover my changes (if applicable).
• [ x ] All new and existing tests passed. (make tests)
• I have updated the documentation (if applicable).
• [ x ] My changes generate no new warnings.
• I have added any necessary new dependencies to pyproject.toml.

Additional Notes

Screenshots (if applicable)