ZIP-244: Create generic transaction id merkle tree

[teor2345]

Is your feature request related to a problem? Please describe.

ZIP-244 defines a new transaction digest algorithm currently planned to be applied from the NU5 network upgrade onward.

ZIP-244 creates non-malleable transaction identifiers that commit to all transaction data except for attestations to transaction validity. (That is, signatures and proofs.)

ZIP-244 also adds a transaction authorization hash, which is hash-chained to the block commitment (#1567) and placed in the block commitment fields.

Describe the solution you'd like

We should implement or integrate this new transaction digest algorithm in Zebra as per:

• https://zips.z.cash/zip-0244
• https://zips.z.cash/zip-0225#modifications-to-zip-244

This will include:

Merkle tree

• refactor our current transaction merkle tree to make it generic. The tree needs to be calculated over:
  • pre-NU5 transaction IDs (before NU5)
  • non-malleable transaction IDs + orchard changes (in NU5 for the block header transaction merkle root field) (TODO)

The transaction authorization hash uses a different merkle tree construction, so it is out of scope for this ticket.

The generic type should be bounded by a TransactionMerkleTree trait, which is implemented by the 3 hash types.

There does not need to be a dependency on the implementation of these types, because we can just define the new types as:

pub struct transaction::non_malleable::Id(pub [u8; 32]);
pub struct transaction::non_malleable::authorization::Hash(pub [u8; 32]);

Alternative Implementations

The ECC have implemented a version of this in Rust in the librustzcash library, we should be able to either port some of that code or learn from that code to implement the Zebra version.

[teor2345]

PR #2129 takes the non-malleable transaction id data from librustzcash, and puts it in Zebra's transaction::Hash type.

So the existing code will work without modification, because we are using the same type for v4 and v5 transaction ids. Therefore this ticket is obsolete.

(If we ever need to check if an id is non-malleable, we can check the transaction version.)