fix: pass memo to deepcopy

[agoose77]

@jpivarski whoops, somehow I missed this on your PR.

[jpivarski]

Right—I can't think of a legitimate case in which an ak.Array instance is inside of the behavior dict, but this is formally correct and if such a situation does show up in the future, this implementation fixes a potential bug.

I'm setting up auto-merge.

[codecov]

Codecov Report

Merging #1698 (eef49bd) into main (e692946) will increase coverage by 0.40%.
The diff coverage is 84.45%.

❗ Current head eef49bd differs from pull request most recent head 6616438. Consider uploading reports for the commit 6616438 to get more accurate results

Additional details and impacted files

Impacted Files	Coverage Δ
src/awkward/_v2/_connect/jax/__init__.py	90.47% <ø> (+1.58%)	⬆️
src/awkward/_v2/config.py	0.00% <0.00%> (ø)
src/awkward/_v2/operations/ak_broadcast_arrays.py	100.00% <ø> (+4.34%)	⬆️
src/awkward/_v2/operations/ak_transform.py	65.51% <ø> (+56.89%)	⬆️
src/awkward/_v2/types/uniontype.py	84.61% <ø> (ø)
src/awkward/_v2/behaviors/categorical.py	73.13% <60.00%> (-8.94%)	⬇️
src/awkward/_v2/contents/bitmaskedarray.py	71.42% <60.00%> (-0.11%)	⬇️
src/awkward/_v2/contents/bytemaskedarray.py	88.32% <60.00%> (-0.03%)	⬇️
src/awkward/_v2/contents/listarray.py	91.89% <60.00%> (-0.02%)	⬇️
src/awkward/_v2/contents/unmaskedarray.py	70.76% <60.00%> (-0.13%)	⬇️
... and 53 more

[agoose77]

NB - this PR is now placing more importance on behavior being None if the user wants ak.behavior - now we deepcopy this, which would be expensive if we are currently passing around ak.behavior explicitly.

[jpivarski]

Presumably, if someone actually says

my_new_array = copy.deepcopy(my_awk_array)

then they don't want my_new_array to share data with my_awk_array.

But, behaviors contain class objects and functions. We don't want them to be copied.

>>> import copy
>>> def some_function(x): return x
... 
>>> class SomeClass: pass
... 
>>> behavior = {"function": some_function, "class": SomeClass, some_function: "as key"}
>>> copied_behavior = copy.deepcopy(behavior)
>>> behavior["function"] is copied_behavior["function"]
True
>>> behavior["class"] is copied_behavior["class"]
True
>>> list(behavior.keys())[2]
<function some_function at 0x1057c7e20>
>>> list(behavior.keys())[2] is list(copied_behavior.keys())[2]
True

Okay: they're not.

[agoose77]

Okay: they're not.

Yes, right now this would only be an issue if a user is passing an instance method (or other non-atomically copied value) into ak.behavior, e.g.

class SpecialAdder:
    def add(self, x, y):
        ...

ak.behavior[np.add, "point", "point"] = SpecialAdder().add

Whilst I don't anticipate this, I think it's worth discussing it up-front in case we this these kinds of issues later.