Merge bitcoindevkit/bdk#1643: feat(chain,wallet)!: rm `ConfirmationTime`

a3d4eef77d427b290e1d0041d3c760b8fe29f6a2 feat(chain,wallet)!: rm `ConfirmationTime` (志宇)

Pull request description:

  ### Description

  This PR removes `ConfirmationTime`, and favors `ChainPosition<ConfirmationBlockTime>` instead. The only difference between these two structures is that `ChainPosition<ConfirmationBlockTime>` contains an additional `BlockHash`. Additionally, `ConfirmationTime` was not used in many places. It was mainly for displaying information in `bdk_wallet::Wallet`.

  We also impl `serde::Deserialize` and `serde::Serialize` for `ChainPosition`.

  ### Notes to the reviewers

  ### Changelog notice

  * Remove `bdk_chain::ConfirmationTime`. Use `ChainPosition<ConfirmationBlockTime>` in place.

  ### 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:
  LagginTimes:
    ACK a3d4eef77d427b290e1d0041d3c760b8fe29f6a2
  oleonardolima:
    ACK a3d4eef77d427b290e1d0041d3c760b8fe29f6a2
  ValuedMammal:
    ACK a3d4eef77d427b290e1d0041d3c760b8fe29f6a2

Tree-SHA512: d94db70885e6987774da586b92ee826098a0da4ae808ff9b23632bd68bbb3d6babbba1aac9d79b78bcf4affa48404f5cca3c7c00ad2db02e1f47f78e094a5f76