Murisi/borsh schemas

[murisi]

Created Borsh schemas for Transactions, Builders, and their subcomponents in order to facilitate their parsing by hardware wallets. More specifically, the changes are as follows:

• Altered the BorshSerialize and BorshDeserialize of ValueSum to match its encoding in Transaction
• Implemented the BorshSchema trait for Transaction, Builder, and their subcomponents.
• Implemented BorshSerialize and BorshDeserialize for most of the structures that now have a BorshSchema. This was done by calling their pre-existing read and write methods. Hence:
  • The (de)serialization of all structures remains unchanged
  • Each structure has exactly one possible serialization
• Fixed the deserialization of Sapling bundles in the case when there are convert descriptions but no spends or outputs
• Fixed the serialization of Sapling bundles in the case when there are no spend, convert, and output descriptions