Merge bitcoindevkit/bdk#1301: Fix `ConfirmationTime` conversion from `ChainPosition`

e687c27096e1c8f36c3a129dc6d92af9c5d05a30 fix(chain): convert to `ConfirmationTime` fix (志宇)

Pull request description:

  ### Description

  We forgot to include the `last_seen` when converting from `ChainPosition` to `ConfirmationTime`.

  ### Notes to the reviewers

  No brainer.

  ### Changelog notice

  * Fix `ConfirmationTime` conversion from `ChainPosition` to include the `last_seen`.

  ### 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

ACKs for top commit:
  LLFourn:
    ACK e687c27096e1c8f36c3a129dc6d92af9c5d05a30

Tree-SHA512: 182f804309c7ea7f2a42911bc00d836ef48a8617c156b2275d6908b07f619b2466039f54728dd3ca2552f4cd11528a8733618f4ce6a4c88d7e88a05a3d82ffaf