Use Address type in address field on AddressInfo

[thunderbiscuit]

This PR leverages the newly exposed methods on the Address type and uses that in the AddressInfo type instead of a address string.

Description

Fixes #332.

Notes to the reviewers

As with the descriptor type, I'm changing the to_string() method to as_string() in the FFI. I don't remember why we made this choice way back when. Is that because of the name clash with the toString() methods on Kotlin and Swift? Just looking for validation before locking the API in.

Changelog notice

API Changes
- address field on `AddressInfo` type is now of type `Address` [#333]

[#333]: https://github.com/bitcoindevkit/bdk-ffi/pull/333

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

[notmandatory]

ACK 5ee8698

Thanks for the extra cleanups !