Move PythonJob out

[superstar54]

This PR moves the PythonJob out aiida-workgraph. And add the aiida-pythonjob package as a dependency.

The PythonJob related data and the serializer have been moved out too.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.95918% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.96%. Comparing base (5937b88) to head (a39787f).
Report is 100 commits behind head on main.

Files with missing lines	Patch %	Lines
aiida_workgraph/engine/utils.py	95.83%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #364      +/-   ##
==========================================
+ Coverage   75.75%   79.96%   +4.20%     
==========================================
  Files          70       61       -9     
  Lines        4615     4846     +231     
==========================================
+ Hits         3496     3875     +379     
+ Misses       1119      971     -148     

Flag	Coverage Δ
python-3.11	79.90% <97.95%> (+4.23%)	⬆️
python-3.12	79.90% <97.95%> (?)
python-3.9	79.95% <97.95%> (+4.22%)	⬆️

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