Improve schema validation

[OCopping]

This PR aims to improve the schema validation by adding the option of adding macros if a custom file is defined in techui.yaml.
It also adds some basic VSCode validation checks (as they are separate from pydantic checks).
And a bit of tidying while I'm at it.

[codecov]

Codecov Report

❌ Patch coverage is 97.67442% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.75%. Comparing base (8bc8482) to head (f6c7304).

Files with missing lines	Patch %	Lines
src/techui_builder/models.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #197      +/-   ##
==========================================
+ Coverage   89.54%   89.75%   +0.20%     
==========================================
  Files           9        9              
  Lines         775      800      +25     
==========================================
+ Hits          694      718      +24     
- Misses         81       82       +1     

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