Merge bitcoindevkit/bdk#2120: fix(chain): forward `confirmation_height_upper_bound...

5d97e136ae89854c53add90d9da9131fec56c4a0 fix(chain): forward `confirmation_height_upper_bound` in `Anchor` impl for `&A` (志宇)

Pull request description:

  ### Description

  The blanket `Anchor` impl for `&A` was missing the `confirmation_height_upper_bound` method, causing it to fall back to the default implementation instead of delegating to the inner type.

  ### Changelog notice

  ```md
  Fixed:

  - The `Anchor::confirmation_height_upper_bound` impl was missing for `&A`, causing it to fallback to the default impl.
  ```

  ### Checklists

  #### All Submissions:

  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)

  #### Bugfixes:

  ~~* [ ] This pull request breaks the existing API~~
  ~~* [ ] I've added tests to reproduce the issue which are now passing~~
  ~~* [ ] I'm linking the issue being fixed by this PR~~

ACKs for top commit:
  ValuedMammal:
    ACK 5d97e136ae89854c53add90d9da9131fec56c4a0
  Dmenec:
    tACK 5d97e136ae89854c53add90d9da9131fec56c4a0

Tree-SHA512: baea97e5adb6fb1953e570339ec6826aa1ed84ff7914c56a4b1480c7df9218c782d7343a458e4f0e2427c12487dddd89cf067f722f868ca0c6584b44d731e56b