Merge bitcoindevkit/bdk#1402: [wallet] Improve address API

d39b319ddf6bf3365d5d01841a8d366c6231db06 test(wallet): Test wallet addresses (valued mammal)
a266b4718f7839759a3e615805931041b67b8e91 chore(wallet)!: Remove enum AddressIndex (valued mammal)
d87874780b4a4c7be282381ae1102c028f3ae581 refactor(wallet)!: Remove method get_address (valued mammal)
d3763e5e37569cea0860217fba980ab0389e4e64 feat(wallet): Add new address methods (valued mammal)

Pull request description:

  Improvements to the wallet address API, see commit messages for details.

  ### Notes to the reviewers

  The logic of getting addresses is roughly the same as before when using `AddressIndex`, following this mapping:

  - `New` -> `reveal_next_address`
  - `LastUnused` -> `next_unused_address` (assuming this is what `LastUnused` really means)
  - `Peek` -> `peek_address`

  Wondering whether it makes sense to expose [`is_used`](https://github.com/bitcoindevkit/bdk/blob/358e842dcda0eb867d229881823c76dba1d7cce1/crates/chain/src/keychain/txout_index.rs#L236) for Wallet as well.

  fixes #898

  ### Changelog notice

  Added:

  - Added Wallet methods:
    - `peek_address`
    - `reveal_next_address`
    - `next_unused_address`
    - `reveal_addresses_to`
    - `list_unused_addresses`
    - `mark_used`
    - `unmark_used`

  Removed:

  - Removed Wallet methods:
    - `get_address`
    - `get_internal_address`
    - `try_get_address`
    - `try_get_internal_address`

  - Removed type AddressIndex

  ### Checklists

  * [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

  ### Feature

  * [x] I've added tests for the new feature
  * [x] I've added docs for the new feature
  * [x] This pull request breaks the existing API
  * [x] I'm linking the issue being fixed by this PR

ACKs for top commit:
  evanlinjin:
    ACK d39b319ddf6bf3365d5d01841a8d366c6231db06

Tree-SHA512: ab7f3031f552ee6ea58ae4f3c5412bbedc0ea63e662fe9fa402de0f68a50448521be1e118e89f70bf970d5bf44ea1dc66bbeeff3e9312bae966bebd3072a7073