Rework sqlite: Instead of only supported one schema (defined in
`bdk_sqlite`), we have a schema per changeset type for more flexiblity.
* rm `bdk_sqlite` crate (as we don't need `bdk_sqlite::Store` anymore).
* add `sqlite` feature on `bdk_chain` which adds methods on each
changeset type for initializing tables, loading the changeset and
writing.
Rework changesets: Some callers may want to use `KeychainTxOutIndex`
where `K` may change per descriptor on every run. So we only want to
persist the last revealed indices by `DescriptorId` (which uniquely-ish
identifies the descriptor).
* rm `keychain_added` field from `keychain_txout`'s changeset.
* Add `keychain_added` to `CombinedChangeSet` (which is renamed to
`WalletChangeSet`).
Rework persistence: add back some safety and convenience when persisting
our types. Working with changeset directly (as we were doing before) can
be cumbersome.
* Intoduce `struct Persisted<T>` which wraps a type `T` which stores
staged changes to it. This adds safety when creating and or loading
`T` from db.
* `struct Persisted<T>` methods, `create`, `load` and `persist`, are
avaliable if `trait PersistWith<Db>` is implemented for `T`. `Db`
represents the database connection and `PersistWith` should be
implemented per database-type.
* For async, we have `trait PersistedAsyncWith<Db>`.
* `Wallet` has impls of `PersistedWith<rusqlite::Connection>`,
`PersistedWith<rusqlite::Transaction>` and
`PersistedWith<bdk_file_store::Store>` by default.
Rework wallet-construction: Before, we had multiple methods for loading
and creating with different input-counts so it would be unwieldly to add
more parameters in the future. This also makes it difficult to impl
`PersistWith` (which has a single method for `load` that takes in
`PersistWith::LoadParams` and a single method for `create` that takes in
`PersistWith::CreateParams`).
* Introduce a builder pattern when constructing a `Wallet`. For loading
from persistence or `ChangeSet`, we have `LoadParams`. For creating a
new wallet, we have `CreateParams`.
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