Merge bitcoindevkit/bdk#2149: `chain 0.23.x`: forward `confirmation_height_upper_boun...

Merge bitcoindevkit/bdk#2149: `chain 0.23.x`: forward `confirmation_height_upper_bound` in `Anchor` implementation for `&A`

00d7f6257715849558c9c22923c183ea6cc3f1e5 fix(chain): forward `confirmation_height_upper_bound` in `Anchor` impl for `&A` (志宇)

Pull request description:

  ### Description

  Backport of #2120
  Depends on #2148

  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)

ACKs for top commit:
  luisschwab:
    ACK 00d7f6257715849558c9c22923c183ea6cc3f1e5
  notmandatory:
    ACK 00d7f6257715849558c9c22923c183ea6cc3f1e5

Tree-SHA512: 919ecc07e82e4c902ba30b576a4617ff63afc17eb4176410dac9abdbec5425a0ba7139312768365386c1d59bd7eb6b733bbae45c8a25d628996135dd226f715f