Merge bitcoindevkit/bdk#1569: Introduce `bdk_core`

a5d076f215cd91173f55bda0d1cc59b9dde75511 chore(core)!: s/tx_graph::Update/TxUpdate/ (LLFourn)
dafb9aaef7d8d4bc83c8ba0845323b92b82fbb3d feat(bitcoind_rpc)!: depend on `bdk_core` instead of `bdk_chain` (志宇)
fea8eede760130db32c2cfaecc272f6c1ed979db feat(esplora)!: depend on `bdk_core` instead of `bdk_chain` (志宇)
0d302f5f204eeac8902a4b5943b9b820c6b575ab feat(electrum)!: depend on `bdk_core` instead of `bdk_chain` (志宇)
ab0315d14fa741a691ee0deef4567ea66cb44a60 feat!: move `spk_client`s to `bdk_core` (志宇)
bdea871a0d0d337772f226fdcf5cd734f3d857ba feat!: move `tx_graph::Update` to `bdk_core` (志宇)
77e31c71a5edc011df42daece1920903bc2b866f feat!: move `CheckPoint` to `bdk_core` (志宇)
a86c878a60f40ce30ab00c0b47fa6cddf30cfe30 refactor(chain): change `CheckPoint::apply_changeset` (志宇)
6f7626ad0bb6ca7e45428af11dbf930d746d9cd0 feat!: introduce `bdk_core` (志宇)

Pull request description:

  Based on #1568
  Closes #1543

  ### Description

  Introduce `bdk_core` crate. Move types over from `bdk_chain`. Chain sources (`bdk_electrum`, `bdk_esplora` and `bdk_bitcoind_rpc`) now only depend on `bdk_core`.

  ### Notes to the reviewers

  Please review commit-by-commit. I've moved things over, but slight API changes were necessary (mentioned in the commit messages).

  ### Changelog notice

  * Add `bdk_core` crate which contains core types that were previously in `bdk_chain`. Including: `BlockId`, `ConfirmationBlockTime`, `CheckPoint`, `CheckPointIter`, `tx_graph::Update` and `spk_client`-types.
  * Change chain sources (`bdk_esplora`, `bdk_electrum` and `bdk_bitcoind_rpc`) to only depend on `bdk_core`.

  ### 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:
    Self-ACK: a5d076f215cd91173f55bda0d1cc59b9dde75511
  evanlinjin:
    ACK a5d076f215cd91173f55bda0d1cc59b9dde75511

Tree-SHA512: 13ecd0a2d2fc840b281977f07dc11fed27459f77c676af470134d2184db4a1fc352073ef82b1622e04fc60edb885e587ae8b9909c9bafb4ae63fcd51325d1cad