fix(rpc): Refactor the serialization of note commitment trees

[upbqdn]

Motivation

Close #8471.

The bug described in #8471 is caused by an incorrect serialization of empty note commitment trees for RPCs. Zebra serializes such trees as the empty string, but zcashd serializes them as 000. This bug is related only to the z_get_treestate RPC. The state contains the right trees and uses a different serialization format.

PR Author Checklist

Check before marking the PR as ready for review:

• [x] Will the PR name make sense to users?
• [x] Does the PR have a priority label?
• [x] Have you added or updated tests?
• [x] Is the documentation up to date?

Solution

• Remove the old RPC serialization code.
• Use the same upstream code as zcashd to serialize the trees for RPCs.
• Cleanups.

Testing

• Remove old test snapshots and add new ones.

Reviewer Checklist

Check before approving the PR:

• [ ] Does the PR scope match the ticket?
• [ ] Are there enough tests to make sure it works? Do the tests cover the PR motivation?
• [ ] Are all the PR blockers dealt with? PR blockers can be dealt with in new tickets or PRs.

And check the PR Author checklist is complete.

Follow Up Work

• #8536