3. refactor(db): add disk serialization types for transactions

[teor2345]

Motivation

We want to:

• Add transparent address indexes to zebra-state #3150
• Store transactions in a separate database index #3151
• Use smaller keys for block and transaction database indexes #3152

To do that, we need to have serialization-specific types for transactions and transparent outputs. And we want to remove duplicate code for height, transaction, and transparent serialization.

Designs

RocksDB section of the state RFC:
https://github.com/ZcashFoundation/zebra/blob/lightwalletd-state-rfc-fix/book/src/dev/rfcs/0005-state-updates.md#rocksdb-data-structures

Some of these types are renamed in this PR, for consistency.

Solution

Code changes:

• simplify block height serialization
• create a TransactionIndex type, and use it in TransactionLocation
• create transparent OutputIndex and OutputLocation types

The disk serialization format is the same, but some of the type names have changed. (These names don't get serialized.)

RFC updates:

• make transparent database type names consistent
• fix a bug in the Utxo.is_coinbase derivation

Review

This PR is based on #3717, GitHub and Mergify should automatically handle the rebase and merge.

Reviewer Checklist

• Code implements design
• Existing tests pass
• Snapshot updates don't change data

Follow Up Work

• Add transparent address indexes to zebra-state #3150
• Store transactions in a separate database index #3151
• Use smaller keys for block and transaction database indexes #3152

[codecov]

Codecov Report

Merging #3741 (b8e96c0) into main (44c7b5d) will decrease coverage by 0.25%.
The diff coverage is 66.39%.

@@            Coverage Diff             @@
##             main    #3741      +/-   ##
==========================================
- Coverage   79.00%   78.74%   -0.26%     
==========================================
  Files         292      292              
  Lines       33311    33379      +68     
==========================================
- Hits        26317    26285      -32     
- Misses       6994     7094     +100     

[dconnolly]

lgtm