[Feature] Enable building valid transactions without submitting them to the network

[iamalwaysuncomfortable]

Motivation

This PR adds the ability to build valid execution transactions without immediately submitting them to the network. This allows transactions to be built beforehand and then later submitted to the network.

The following methods have been introduced to build transactions offline. Each will return a Transaction object which is a wasm object representing an Aleo transaction. Users can use the toString() method on this object to get a human readable string representation of the Transaction.

buildExecutionTransaction - Build an execution transaction for an arbitrary execution
buildTransferTransaction - Build an transfer transaction for any of the 4 transaction types
buildTransferPublicTransaction - Build a transfer public transaction
buildBondPublicTransaction - Build a bond public transaction to bond as a delegator or validator to the network
buildUnbondPublicTransaction - Build an unbond public transaction
buildClaimUnbondPublicTransaction - Build a transaction to claim unbonded stake

If the fee for a transaction is paid publicly (with the fee_public method) and the function being executed doesn't take any records as input, the transaction can be built completely offline without connection to the internet.