test: improve vns utils test coverage to 100%

[ifavo]

Description

This Pull Requests adds testing for the vnsUtils to ensure configuration errors are handled as expected and contract calls use the correct signature.

Fixes #885

Type of change

Please delete options that are not relevant.

– Test Coverage

How Has This Been Tested?

yarn solo:test
yarn merge-coverage

• Verify manually on coverage report at ../network/src/utils/vns that the coverage is 100%

Test Configuration:

• Node.js Version: v18.20.2
• Yarn Version: 3.6.1

Checklist:

• [x] My code follows the coding standards of this project
• [x] I have performed a self-review of my code
• [x] I have commented on my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] New and existing integration tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules
• [x] I have not added any vulnerable dependencies to my code