c7b47af72f
Previously `SpkTxOutIndex` methods can be called from `KeychainTxOutIndex` due to the `DeRef` implementation. However, the internal `SpkTxOut` will also contain lookahead spks resulting in an error-prone API. `SpkTxOutIndex` methods are now not directly callable from `KeychainTxOutIndex`. Methods of `KeychainTxOutIndex` are renamed for clarity. I.e. methods that return an unbounded spk iter are prefixed with `unbounded`.