Merge bitcoindevkit/bdk#1454: Refactor wallet and persist mod, remove bdk_persist...

ec36c7eccacc8347568b77ed1dfc0c50a2524906 feat(example): use changeset staging with rpc polling example (志宇)
19328d4999c19557778b7b108f88f42b1258957e feat(wallet)!: change persist API to use `StageExt` and `StageExtAsync` (志宇)
2e40b0118cc88539f38420e347eb4d562b1be0b1 feat(chain): reintroduce a way to stage changesets before persisting (志宇)
36e82ec6869c5c5c5669d4d049636225f9a8e986 chore(chain): relax `miniscript` feature flag scope (志宇)
9e97ac03307f3194e043ef430e4bde2e5c25254c refactor(persist): update file_store, sqlite, wallet to use bdk_chain::persist (Steve Myers)
54b0c11cbe1d08eb955e50f0ac719a0b19e3032a feat(persist): add PersistAsync trait and StagedPersistAsync struct (Steve Myers)
aa640ab2770bea19259eedea6882b202a5845f35 refactor(persist): rename PersistBackend to Persist, move to chain crate (Steve Myers)

Pull request description:

  ### Description

  Sorry to submit another refactor PR for the persist related stuff, but I think it's worth revisiting. My primary motivations are:

  1. remove `db` from `Wallet` so users have the ability to use `async` storage crates, for example using `sqlx`. I updated docs and examples to let users know they are responsible for persisting changes.
  2. remove the `anyhow` dependency everywhere (except as a dev test dependency). It really doesn't belong in a lib and by removing persistence from `Wallet` it isn't needed.
  3. remove the `bdk_persist` crate and revert back to the original design with generic error types. I kept the `Debug` and `Display` constrains on persist errors so they could still be used with the `anyhow!` macro.

  ### Notes to the reviewers

  I also replaced/renamed old `Persist` with `StagedPersist` struct inspired by #1453, it is only used in examples. The `Wallet` handles it's own staging.

  ### Changelog notice

  Changed

  - Removed `db` from `Wallet`, users are now responsible for persisting changes, see docs and examples.
  - Removed the `bdk_persist` crate and moved logic back to `bdk_chain::persist` module.
  - Renamed `PersistBackend` trait to `Persist`
  - Replaced `Persist` struct with `StagedPersist`

  ### 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:
  ValuedMammal:
    ACK ec36c7eccacc8347568b77ed1dfc0c50a2524906

Tree-SHA512: 380b94ae42411ea174720b7c185493c640425f551742f25576a6259a51c1037b441a238c6043f4fdfbf1490aa15f948a34139f1850d0c18d285110f6a9f36018