These exist in Cashtab. Currently any app that wants to accept or cancel utxos needs to do this. `ecash-agora` does expose helpful methods for getting the fee. But, we might as well have this too, esp since `chronik-client` is already a dependency and the utxos are themselves strongly typed.
These functions and tests are copied from Cashtab.
TODO
[] Implement in Cashtab in this diff to show it works
[] Update changelog link