scenario1:
- 2of2 multisig wallet with trezor1 and trezor2 keystores
- only trezor2 connected
- previously we would pair first keystore with connected device and then display error.
now we will pair the device with the correct keystore on the first try
scenario2:
- standard wallet with trezor1 keystore
- trezor2 connected (different device)
- previously we would pair trezor2 with the keystore and then display error.
now we will prompt the user to select which device to pair with (out of one)
related: #5789
previously, client.handler was sometimes
- an InstallWizard
- a QtHandlerBase where win was an ElectrumWindow
- a QtHandlerBase where win was an InstallWizard
- a CmdLineHandler
That's just too much dynamic untyped undocumented polymorphism...
Now it will never be an InstallWizard (replaced with QtHandlerBase where win is an InstallWizard),
and now in all cases client.handler is an instance of HardwareHandlerBase, yay.
related: #6063
this is a regression from #5721
Removed the `TxInput.is_coinbase` method as I think it is a confusing API,
instead we now have `TxInput.is_coinbase_input` and `TxInput.is_coinbase_output`.
related #5872
we should not raise generic Exception when wanting to communicate with
the user. it makes distinguishing programming errors and messages hard,
as the caller will necessarily need to catch all Exceptions then
