This replaces `bdk_chain::PersistWith` which wanted to persist anything
(not only `Wallet`), hence, requiring a whole bunch of generic
parameters.

Having `WalletPersister` dedicated to persisting `Wallet` simplifies the
trait by a lot.

In addition, `AsyncWalletPersister` has proper lifetime bounds whereas
`bdk_chain::PersistAsyncWith` did not.

Changeset methods `.persist_to_sqlite` and `from_sqlite` no longer
internally call `.init_sqlite_tables`. Instead, it is up to the caller
to call `.init_sqlite_tables` beforehand.

This allows us to utilize `WalletPersister::initialize`, instead of
calling `.init_sqlite_tables` every time we persist/load.

Introduce `Wallet::staged_mut` method.

This forces the caller to use the same persister type that they used for
loading/creating when calling `.persist` on `PersistedWallet`.

This is not totally fool-proof since we can have multiple instances of
the same persister type persisting to different databases. However, it
does further enforce some level of safety.