The fee rule used in constructing a Proposal

A data structure that describes a series of transactions to be created.

A data structure that describes the inputs to be consumed and outputs to
be produced in a proposed transaction.

A mapping from ZIP 321 payment index to the output pool that has been chosen
for that payment, based upon the payment address and the selected inputs to
the transaction.

The unique identifier and value for each proposed input that does not
require a back-reference to a prior step of the proposal.

A reference a payment in a prior step of the proposal. This payment must
belong to the wallet.

A reference a change output from a prior step of the proposal.

The unique identifier and value for an input to be used in the transaction.

The proposed change outputs and fee value.

A proposed change output. If the transparent value pool is selected,
the `memo` field must be null.

An object wrapper for memo bytes, to facilitate representing the
`change_memo == None` case.