gh-145876: Fix AttributeError masked during dict unpacking

[ashm-dev]

Summary

• Check .keys attribute existence before calling PyDict_Update/_PyDict_MergeEx in DICT_UPDATE and DICT_MERGE bytecodes
• Remove overly broad AttributeError catch that was masking real errors as TypeError: 'X' object is not a mapping

Closes #145876.

• Issue: AttributeErrors raised in .keys() or .__getitem__() during {**mymapping}are incorrectly masked #145876

[picnixz]

I suspect that this will add an overhead to non-exact dict operations. It's definitely not desirable in this case. In addition, the case is a bit niche IMO. I want to discuss this on the issue first so I'm going to close it for now.

[bedevere-app]

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