A possible issue with not deepcopying job kwargs

[vineetbansal]

As we discovered when working towards another PR, mutating one job's config mutates all others created by that decorator. This is because the @job decorator keeps a reference to job_kwargs instead of deep-copying it. This may or may not be an issue, and may just need explicit documentation.

This PR introduces an xfail test to demonstrate this behavior. The solution suggested by @gpetretto which should solve this is:

--- a/src/jobflow/core/job.py
+++ b/src/jobflow/core/job.py
@@ -184,6 +184,7 @@ def job(
     --------
     Job, .Flow, .Response
     """
+    from copy import deepcopy

     def decorator(func):
         from functools import wraps
@@ -214,7 +215,7 @@ def job(
                         args = args[1:]

             return Job(
-                function=f, function_args=args, function_kwargs=kwargs, **job_kwargs
+                function=f, function_args=args, function_kwargs=kwargs, **deepcopy(job_kwargs)
             )