PyQt translates python integers to signed 32 bits int when emitting a `int` in a signal. Make the signal emit a generic object instead, to avoid an integer overflow. This signal is emitted infrequently, when the user loads a proof, loads coins or deletes coin from a proof, so there should be no significant performance impact here.
This issue was seen before in the selected amount tool: https://github.com/Bitcoin-ABC/ElectrumABC/pull/291