Other changes:
* The `async-https` feature of `bdk_esplora` is no longer default.
* Rename `ObservedAs` to `ChainPosition`.
* Set temporary MSRV to 1.60.0 to compile all workspace members will all
features.
* `ElectrumUpdate::missing_full_txs` now returns a `Vec<Txid>` so we
don't keep a reference to the passed-in `graph`.
* `ElectrumUpdate::finalize*` methods now takes in `missing` txids
instead of `full_txs`. `Client::batch_transaction_get` is called
within the methods.
Other changes:
* `wallet::ChangeSet` is now made public externally. This is required as
a wallet db should implement `PersistBackend<wallet::ChangeSet>`.
This corresponds to `keychain::KeychainChangeSet` but for the redesigned
structures with `LocalChain`.
This structure is now used in `Wallet` as well as the examples.
