As observed in recent attempts to develop a simple tx building demo for new devs looking to build on eCash, there are a number of chronik specific nuances that the app dev needs to handle in their app.
One such nuance is where chronik-client's `.script().utxos()` api returns a mixture of both XEC and SLP UTXOs, which meant the app developer would have to explicitly filter in their app.
This diff keeps the existing `outputScript` and `utxos` attributes to maintain backwards compatibility, but adds new `xecUtxos` and `slpUtxos` attributes which are essentially a filter applied on the `utxos` map array based on whether the `slpToken` param exists or not.
This `slpToken` param determines whether the utxo is a token utxo or not, however worth noting that this only applies to the Chronik indexer, hence why it's worth abstracting this indexer specific knowledge from app devs.