`ecash-lib` requires tx builder outputs to have a `script: <Script>` key, not an `address: <cashaddr>` key. Currently we are converting all targetOutputs in the sendXec function.
Going forward, we will start to support more complicated txs that may have `targetOutputs` already fully prepared (e.g. with a custom `p2sh` `Script` from `ecash-agora`. Rather than only convert some targetOutputs and not others in `sendXec`, we should instead prepare all targetOutputs to the same `ecash-lib` standard.
With added support in `ecash-lib` for converting an address to a `Script` now available, we can now prepare all Cashtab `targetOutputs` for `ecash-lib` so that they do not need to go through a Cashtab-specific conversion process at the tx build step.