Merge bitcoindevkit/bdk#1652: refactor(chain)!: remove `inner` method from KeychainTx...

8494c12ed49856b069375bdb036e6036c77f9019 refactor(chain)!: remove `inner` method from KeychainTxOutIndex (valued mammal)

Pull request description:

  Fix #1353 by removing the `inner` method from `keychain_txout` module. See commit message for details.

  ### Changelog notice

  - `bdk_chain`: Removed method `KeychainTxOutIndex::inner`

  ### 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
  * [x] This pull request breaks the existing API
  * [x] I'm linking the issue being fixed by this PR

ACKs for top commit:
  oleonardolima:
    ACK 8494c12ed49856b069375bdb036e6036c77f9019
  notmandatory:
    ACK 8494c12ed49856b069375bdb036e6036c77f9019

Tree-SHA512: f0f6864faa16ffcd49f63c7a38cba11f28ad8f7c7aecc8e7538b7d5862a51d43ee75bea81561236ba7876b5e3d6357a021d17212295c5c9ff9a5525aea586953