Fix variable defaulting resolution bug/ remove deprecated overridestring/ enhance testing

[davidgamero]

Description

Fixes a current bug where variable defaults are not resolved properly for references

Added unit tests for prompting logic and default resolution to avoid this issue in the future

Refactor prompt package to allow better testing by adding parameters for Stdin and Stdout with defaults on nil to follow promptui library convention

Remove deprecated overridestring structs

Type of change

Please delete options that are not relevant.

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

How Has This Been Tested?

• [x] Existing tests pass
• [x] Added unit tests for string prompting
• [x] Added unit tests for variable defaulting resolution

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] 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] Any dependent changes have been merged and published in downstream modules