Reuse electrum clients #488
Description
In #486, we added initial support for sourcing chain data from an Electrum server based on rust-electrum-client.
As the respective sync clients in lightning-transaction-sync and bdk_electrum currently don't allow to take clients by reference, we were currently forced to create three separate clients (read: connections to the server). Once all sides shipped the respective fixes (bitcoindevkit/rust-electrum-client#163 / lightningdevkit/rust-lightning#3646), we should reuse a single connection.