Add back HWI signing support

**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