Expose Wallet::create_single method

[thunderbiscuit]

This PR exposes the Wallet::create_single() method.

I prefer to use single-descriptor wallets for my Tatooine faucet (easier to sync and keep track of), and realized we didn't bring this back into the bindings API after it was merged in Rust a while back.

TODO: Needs at least a test or two! Some methods should fail I think when the wallet is a single-descriptor, so we can test for that too.

Changelog notice

Added:
    - Expose `Wallet::create_single` constructor on Wallet type [#825]

[#825]: https://github.com/bitcoindevkit/bdk-ffi/pull/825

Checklists

All Submissions:

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

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

[reez]

nice! looking pretty good, good addition.

a couple small comments questions added above.

then also a suggestion here would maybe be to add in error.rs:

impl From<BdkCreateWithPersistError<PersistenceError>> for CreateWithPersistError {
    fn from(error: BdkCreateWithPersistError<PersistenceError>) -> Self {
        match error {
            BdkCreateWithPersistError::Persist(e) => CreateWithPersistError::Persist {
                error_message: e.to_string(),
            },
            BdkCreateWithPersistError::Descriptor(e) => CreateWithPersistError::Descriptor {
                error_message: e.to_string(),
            },
            BdkCreateWithPersistError::DataAlreadyExists(_e) => {
                CreateWithPersistError::DataAlreadyExists
            }
        }
    }
}

so we can use .map_err(CreateWithPersistError::from)?; in wallet.rs instead of:

                .map_err(|e| CreateWithPersistError::Persist {
                    error_message: e.to_string(),
                })?;

Not a blocker though.

[thunderbiscuit]

Great idea @reez on cleaning up the errors on the constructor. I added that fix in a second commit. Ready for re-review!

[reez]

ACK 53d4986

Good addition