Split dust errors

[gemcoder21]

inside core

[DRadmir]

@0xh3rman

In WalletCore flow we differentiate two UTXO dust cases via Error_dust_amount_requested (the amount itself is below the dust threshold) vs Error_not_enough_utxos (the leftover change would be dust). In the new native planner both look like they collapse into SignerError::invalid_input("invalid transaction amount") / "insufficient balance". Is it possible to keep these as two distinct variants in SignerError so we can differentiate them on the client?

[0xh3rman]

Currently gemstone returns 2 different error messages, what else needs to be done? @DRadmir