Move to src folder

[superstar54]

After moving the wdiget and the web app out aiida-workgraph, we can move the aiida-workgraph folder to the src folder.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.59%. Comparing base (c0b5db5) to head (2b597d0).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #377      +/-   ##
==========================================
+ Coverage   89.57%   89.59%   +0.02%     
==========================================
  Files          61       61              
  Lines        4507     4507              
==========================================
+ Hits         4037     4038       +1     
+ Misses        470      469       -1     

Flag	Coverage Δ
python-3.11	89.52% <ø> (ø)
python-3.12	89.54% <ø> (+0.02%)	⬆️
python-3.9	89.56% <ø> (ø)

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