If the Bridge is unavailable, on my machine it takes 2 seconds to timeout.
i.e. call_bridge("enumerate") and BridgeTransport.enumerate() both take 2 seconds each.
With this change, if the Bridge is unavailable, DeviceMgr.scan_devices() takes 4 seconds less.
In below log, with 6 different hw devices connected, scan time was originally ~7.5 seconds;
with this change it became ~3.5 seconds.
Now the time is dominated by WebUsbTransport.enumerate(), called by Trezor,
KeepKey, SafeT, ~1.1 seconds each.
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I | plugin.DeviceMgr | scan_devices() entered. 1598666278.6756
I | plugin.DeviceMgr | scan_devices(). _scan_devices_with_hid() DONE. 1598666278.7583
I | plugin.DeviceMgr | scan_devices(). starting custom enumeration loop. 1598666278.7593
I | plugin.DeviceMgr | scan_devices(). custom enumeration iter DONE, for <bound method SafeTPlugin.enumerate of <electrum.plugins.safe_t.qt.Plugin object at 0x000001F60060A730>>. 1598666279.9345
I | plugins.trezor.qt.Plugin | trezor custom enumeration entered. 1598666279.9345
I | plugins.trezor.qt.Plugin | trezor custom enumeration. call_bridge('enumerate') DONE. 1598666281.9385
>> trezorlib enumerating <class 'trezorlib.transport.bridge.BridgeTransport'> DONE at 1598666283.9500.
>> trezorlib enumerating <class 'trezorlib.transport.webusb.WebUsbTransport'> DONE at 1598666285.0427.
>> trezorlib enumerating <class 'trezorlib.transport.hid.HidTransport'> DONE at 1598666285.1198.
>> trezorlib enumerating <class 'trezorlib.transport.udp.UdpTransport'> DONE at 1598666285.1237.
I | plugins.trezor.qt.Plugin | trezor custom enumeration. trezorlib.transport.enumerate_devices() DONE. 1598666285.1257
I | plugin.DeviceMgr | scan_devices(). custom enumeration iter DONE, for <bound method TrezorPlugin.enumerate of <electrum.plugins.trezor.qt.Plugin object at 0x000001F60C16F4C0>>. 1598666285.1257
I | plugin.DeviceMgr | scan_devices(). custom enumeration iter DONE, for <bound method KeepKeyPlugin.enumerate of <electrum.plugins.keepkey.qt.Plugin object at 0x000001F60BADF130>>. 1598666286.2251
I | plugin.DeviceMgr | scan_devices(). custom enumeration iter DONE, for <bound method ColdcardPlugin.detect_simulator of <electrum.plugins.coldcard.qt.Plugin object at 0x000001F60BAA5AC0>>. 1598666286.2251
I | plugin.DeviceMgr | scan_devices(). custom enumeration loop DONE. 1598666286.2251
I | plugin.DeviceMgr | scan_devices(). find out what was disconnected DONE. 1598666286.2251
I | plugin.DeviceMgr | scan_devices(). Unpair disconnected devices DONE. 1598666286.2251
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