Merge bitcoindevkit/bdk#1812: fix(wallet): use `map_keychain` in `Wallet::build_fee_bump`

Merge bitcoindevkit/bdk#1812: fix(wallet): use `map_keychain` in `Wallet::build_fee_bump`

515309e99fb92335a35ef994839a37a26f23ea69 test(wallet): test `build_fee_bump` with single descriptor wallet (valued mammal)
53d16e1b38eabee1f1ca304933a818951b8b0f43 fix(wallet): use `map_keychain` in `Wallet::build_fee_bump` (valued mammal)

Pull request description:

  Previously we failed to remove the change output if the wallet has no internal keychain which caused tx building to fail at the new higher feerate. Fix this by mapping the internal keychain to the de-facto change keychain so that the drain output can be recalculated.

  fixes #1807

  ### Changelog notice

  Fixed

  - wallet: Fixed an issue preventing `build_fee_bump` from re-targeting the drain value for some wallets

  ### 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

  #### Bugfixes:

  * [x] I've added tests to reproduce the issue which are now passing
  * [x] I'm linking the issue being fixed by this PR

ACKs for top commit:
  notmandatory:
    ACK 515309e99fb92335a35ef994839a37a26f23ea69
  evanlinjin:
    ACK 515309e99fb92335a35ef994839a37a26f23ea69

Tree-SHA512: 53266c4b0f4a2ebc1fd47cd1c9afb4499fb3c46d75e8bd121a98644cfe879cebf5fa26fab0e6af706452aea79a959660149582dc8df9e53ada6582e62ea5be19