Fix mypy errors (extensions)

[Randl]

Summary

Following discussion, I'm splitting #8187 by module.

Details and comments

This fixes all the mypy errors in extensions as for now. Since the assignment to undefined attribute is the purpose of this code, I don't see better solution than just ignore those errors

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[AngeloDanducci]

Took a look at this with mypy version 1.2.0 and I didn't see the corresponding errors on main, or on the commit prior to this one.

If you can reproduce them on 1.2.0 this seems like good low hanging fruit, but both without options and with the options I found in the discussion earlier (--ignore-missing-imports --no-strict-optional --allow-untyped-globals --allow-redefinition --show-error-codes) I couldn't see the errors this would fix.

[Randl]

I do get these with

dmypy run -- --ignore-missing-imports --no-strict-optional --allow-untyped-globals --allow-redefinition --show-error-codes qiskit

Though there was some discussion with @Cryoris @kevinsung regarding not including ignores as for now. In this case we should just close this one for now