Convert logic to allow for validation

[OCopping]

This PR reworks some logic of the autofill script to remove the need for a index-src.bob file. Instead of specifically looking for macros to replace, we will just overwrite the contents of the xml tag with anything provided by the user in the techui.yaml.

The next step will be to implement full validation for every user-edited screen, instead of just index.bob.

[codecov]

Codecov Report

❌ Patch coverage is 20.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.03%. Comparing base (7600a81) to head (d79760f).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/techui_builder/autofill.py	20.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #159      +/-   ##
==========================================
+ Coverage   81.92%   82.03%   +0.11%     
==========================================
  Files           7        7              
  Lines         581      579       -2     
==========================================
- Hits          476      475       -1     
+ Misses        105      104       -1     

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