Fix network patch with negative eigen value

[Neylix]

Description

Fixes an issue where in certain case (low number of nodes and low latencies) the eigen values calulated during network patch algo was negative causing a NaN value after.

Fixed it using the absolute value of the eigen value.

Also added default value for the network patch to avoid serialization issue

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Tested using this matrix:

[
   [0, 18, 3],
   [18, 0, 2],
   [3, 2, 0]
]

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules