add register_pickle_by_value

[superstar54]

By enabling register_pickle_by_value=True, the function is serialized by value instead of being referenced by its module path. This embeds the function unpickled even if the original module is unavailable on the remote computer.

Note: If the function contains import statements, the imported modules must still be installed on the remote computer.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.04%. Comparing base (839e3ba) to head (6cfca02).

Files with missing lines	Patch %	Lines
src/aiida_pythonjob/utils.py	90.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
+ Coverage   87.88%   88.04%   +0.16%     
==========================================
  Files          14       14              
  Lines         652      661       +9     
==========================================
+ Hits          573      582       +9     
  Misses         79       79              

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