Add back HWI signing support

[notmandatory]

Describe the enhancement

As part of the 1.0 update we removed HWI signing support. The original support was using the python based HWI library. We should use the Wizardsardine async-hwi tool to re-add this capability.

Use case

This will provide an example for how to integrate bdk_wallet with the async-hwi library and allow bdk-cli users to experiment and test with different hardware signers that it supports.

Additional context

https://github.com/wizardsardine/async-hwi