We remove `ElectrumUpdate` and return tuples instead for `ElectrumExt` methods. We introduce the `IncompleteTxGraph` structure to specifically hodl the incomplete `TxGraph`. This change is motivated by @LLFourn's comment: https://github.com/bitcoindevkit/bdk/pull/1084/commits/794bf37e637d3266b75827678f015e14f827d318#r1305432603
BDK Electrum
BDK Electrum client library for updating the keychain tracker.