PythonJob spports exit code output

[superstar54]

This PR allows custom exit_code for PythonJob. Add a built-in output socket, exit_code, which serves as a mechanism for error handling and status reporting during task execution. This exit_code is dict with status and message. For the status, an integer value where 0 indicates a successful completion, and any non-zero value signals that an error occurred.

How it Works:

When the function returns a dictionary with an exit_code key, the system automatically parses and uses this code to indicate the task's status. In the case of an error, the non-zero exit_code value helps identify the specific problem.

Benefits of exit_code:

1. Error Reporting:
   If the task encounters an error, the exit_code can communicate the reason. This is helpful during process inspection to determine why a task failed.

2. Error Handling and Recovery:
   You can utilize exit_code to add specific error handlers for particular exit codes. This allows you to modify the task's parameters and restart it.

Below is an example Python function that uses exit_code:

from aiida_workgraph import WorkGraph, task

@task.pythonjob(outputs=[{"name": "sum"}])
def add(x: int, y: int) -> int:
    sum = x + y
    if sum < 0:
        exit_code = {"status": 1, "message": "Sum is negative"}
        return {"sum": sum, "exit_code": exit_code}
    return {"sum": sum}

wg = WorkGraph("test_PythonJob")
wg.add_task(add, name="add", x=1, y=-2)
wg.submit(wait=True)

print("exit status: ",  wg.tasks["add"].node.exit_status)
print("exit message: ",  wg.tasks["add"].node.exit_message)

>>> WorkGraph process created, PK: 146751
>>> exit status:  1
>>> exit message:  Sum is negative

In this example, the task failed with exit_code = 1 due to the condition Sum is negative, which is also reflected in the state message.

> verdi process show 146718                                                               (aiida) 
Property     Value
-----------  ------------------------------------
type         PythonJob<add>
state        Finished [1] Sum is negative
pk           146718
uuid         2ffe92ed-0634-4a02-95fe-c14ecb778f92
label        add
description
ctime        2024-09-09 13:21:14.818233+02:00
mtime        2024-09-09 13:21:18.138330+02:00
computer     [1] localhost

Here is another example form PW calculation

> verdi process show 146793                                                             (aiida) 
Property     Value
-----------  --------------------------------------------------------------------------------
type         PythonJob<scf>
state        Finished [410] The electronic minimization cycle did not reach self-consistency.
pk           146793
uuid         5ed2228d-42ca-46f2-8e7f-d862c6991fba
label        scf

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 79.54545% with 18 lines in your changes missing coverage. Please review.

Project coverage is 80.69%. Comparing base (5937b88) to head (45d1c0f).
Report is 66 commits behind head on main.

Files with missing lines	Patch %	Lines
aiida_workgraph/tasks/pythonjob.py	71.79%	11 Missing ⚠️
tests/test_python.py	77.27%	5 Missing ⚠️
aiida_workgraph/calculations/python_parser.py	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #300      +/-   ##
==========================================
+ Coverage   75.75%   80.69%   +4.94%     
==========================================
  Files          70       66       -4     
  Lines        4615     4947     +332     
==========================================
+ Hits         3496     3992     +496     
+ Misses       1119      955     -164     

Flag	Coverage Δ
python-3.11	80.61% <79.54%> (+4.94%)	⬆️
python-3.12	80.61% <79.54%> (?)
python-3.9	80.65% <79.54%> (+4.91%)	⬆️

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