Merge bitcoindevkit/bdk#1595: refactor(wallet): use `Amount` everywhere

Merge bitcoindevkit/bdk#1595: refactor(wallet): use `Amount` everywhere

292ec3cb3a41d7b9f42cfea536c39b27dba16d4c refactor(wallet): use `Amount` everywhere (valued mammal)

Pull request description:

  This is a followup to #1426 that refactors wallet internals to use `bitcoin::Amount` (nearly) everywhere. I chose not to change any public types in `coin_selection.rs` that still use `u64` as that might require more discussion.

  partially addresses #1432
  fixes #1434

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  oleonardolima:
    ACK 292ec3cb3a41d7b9f42cfea536c39b27dba16d4c
  notmandatory:
    ACK 292ec3cb3a41d7b9f42cfea536c39b27dba16d4c

Tree-SHA512: e84c543e796e151803321ad238023bd5f446448b4430dd6c62929180d159ee1ef867e98f69a4ef3b152c3146b8e30bbf01ce7952ac00b726847a224dca7e3be4