refactor: review & simplify nsc/builder/build.py

[thomaschristory]

Scope

nsc/builder/build.py (514 lines) — translates a parsed OpenAPI schema into a CommandModel.

Goal

Code review + simplify pass:

• Look for transformation steps that can be broken into smaller, testable functions
• Identify any logic leaking concern boundaries (builder touching CLI or HTTP concepts)
• Remove over-engineered fallback paths
• Ensure mypy --strict compliance throughout

Files

• nsc/builder/build.py
• Related tests: tests/builder/

[thomaschristory]

Claiming #49. Branch: refactor/builder-simplify. Reviewing nsc/builder/ for dead branches, over-defensive conditionals, Any escapes, what-comments.

[thomaschristory]

Done. PR: #69