feat: example using hwi signing with

[sdmg15]

Description

Integrates a new BDK signer using async-hwi.
The included example uses Bitbox02 but can be easily extended to use any other supported device.

Notes for reviewer

It's related to issue #20

Changelog notice

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

[notmandatory]

Thanks for this! looks like a good simple example for using hwi-async with bdk_wallet. One FYI we are talking about removing signing from bdk_wallet and delegating it to the rust-bitcoin Psbt::sign function. How hard would it be to use hwi-async to just sign a Psbt ?

[sdmg15]

async-hwi provides a function with the following signature

    async fn sign_tx(&self, tx: &mut Psbt) -> Result<(), Error>;

So I think after constructing the psbt we can just call that function and voila.

[sdmg15]

So at this level we can just call bibox_signer.sign(psbt) given that the psbt has been constructed with bdk_wallet or something else

[notmandatory]

Yes I think this is the right approach. Even though it makes the example much simpler it's still useful to show the end-to-end flow of using async-hwi to sign a psbt created with bdk_wallet::TxBuilder (and eventually the bdk_tx::TxBuilder).

[sdmg15]

Is it a good idea to add syncing wallet code in the example?
If not what's a good way of mocking the wallet with some utxos to sign?

[sdmg15]

@notmandatory
Instead of syncing I "mocked" the wallet with some UTXOs since syncing isn't the goal of this example.

I also added a feature simulator when enabled for people that don't have a physical device connected but still want to run the example (Still need to add instructions on the readme on how to run)

Please let me know what you think