gh-137681: Always initialize exception handler for new instruction

[DinoV]

basicblock_addop zero initializes some members but not all. If we remove some nops and then later re-add an instruction we can have previously initialized memory that can include an exception handler. If we compile something like:

def foo():
    try:
        [x for x in abc]
    except OSError:
        pass

    return```

We'll end up with different exception handling table because the `NOT_TAKEN` instruction is inserted after we do the exception handling analysis and gets a previously initialized exception handler.

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* Issue: gh-137681
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[iritkatriel]

This change is fine, but I think basicblock_addop should get the target and except as args. There is a future bug here where setting the except matters, and someone will forget.

[DinoV]

This change is fine, but I think basicblock_addop should get the target and except as args. There is a future bug here where setting the except matters, and someone will forget.

Do you think we should back port this to 3.14? While the NOT_TAKEN case is pretty benign I'm a little worried there could be something inserted where it does matter.

[iritkatriel]

If we don't have a bug in 3.14 I think we can leave it alone. We're not likely to insert new bytecode transformations there.