chore(skills): Add unit guide skill

[joefernandez]

Creating Skill for generating code unit guides. See skill description for details

Testing Plan

Not applicable

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• [n/a] I have added tests that prove my fix is effective or that my feature works.
• [n/a] New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.