Fix bug with pickling PointFunc

[jessegrabowski]

Description

Fixes a bug when unpickling certain step samplers (BinaryMetropolis, BinaryGibbsMetropolis, and CategoricalGibbsMetropolis) when mp_ctx is spawn or forkserver

Related Issue

• Closes Cannot unpickle certain step samplers when mp_ctx=spawn or forkserver #7857
• Related to #

Checklist

• Checked that the pre-commit linting/style checks pass
• Included tests that prove the fix is effective or that the new feature works
• Added necessary documentation (docstrings and/or example notebooks)
• If you are a pro: each commit corresponds to a relevant logical change

Type of change

• New feature / enhancement
• Bug fix
• Documentation
• Maintenance
• Other (please specify):

[ricardoV94]

Why is this specific to binary gibbs? That's the only one using PointFunc?

We should test spawning a PointFunc instead or this test won't be a regression test if binary gibbs changes to not using PointFunc

[jessegrabowski]

no idea why it's these functions. model.compile_xxx returns a PointFunc, so everyone uses them, but only these 3 samplers trigger the error (I tried most of them)

[ricardoV94]

Most samplers build their own function on raveled inputs and don't use the wrapper PointFunc for performance

[ricardoV94]

Just to be sure this failed before?

[jessegrabowski]

Yep

FAILED                         [100%]
tests/test_pytensorf.py:769 (test_pickle_point_func)
def test_pickle_point_func():
        """
        Regression test for https://github.com/pymc-devs/pymc/issues/7857
        """
        import cloudpickle
    
        x, y = pt.vectors("x", "y")
        outs = x * 2 + y**2
        f = compile([x, y], outs)
    
        point_f = PointFunc(f)
        point_f_pickled = cloudpickle.dumps(point_f)
>       point_f_unpickled = cloudpickle.loads(point_f_pickled)
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

test_pytensorf.py:782: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../pymc/pytensorf.py:573: in __getattr__
    return getattr(self.f, item)
                   ^^^^^^
../pymc/pytensorf.py:573: in __getattr__
    return getattr(self.f, item)
                   ^^^^^^
../pymc/pytensorf.py:573: in __getattr__
    return getattr(self.f, item)
                   ^^^^^^
E   RecursionError: maximum recursion depth exceeded
!!! Recursion detected (same locals & position)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.98%. Comparing base (ae43026) to head (55db526).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7858      +/-   ##
==========================================
+ Coverage   92.92%   92.98%   +0.06%     
==========================================
  Files         107      108       +1     
  Lines       18299    18328      +29     
==========================================
+ Hits        17004    17043      +39     
+ Misses       1295     1285      -10     

Files with missing lines	Coverage Δ
pymc/pytensorf.py	90.02% <100.00%> (ø)

... and 20 files with indirect coverage changes

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