Added submodules, with tests for guibuilder

[adedamola-sode]

Added submodules,
Separated datatypes and gui builder functionality
Added tests

[codecov]

Codecov Report

Attention: Patch coverage is 90.29126% with 10 lines in your changes missing coverage. Please review.

Project coverage is 91.45%. Comparing base (10409c0) to head (6ee200e).

Files with missing lines	Patch %	Lines
src/phoebus_guibuilder/guibuilder.py	87.69%	8 Missing ⚠️
src/phoebus_guibuilder/__main__.py	50.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #24       +/-   ##
===========================================
+ Coverage   52.00%   91.45%   +39.45%     
===========================================
  Files           3        4        +1     
  Lines         100      117       +17     
===========================================
+ Hits           52      107       +55     
+ Misses         48       10       -38     

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