* refactor(db): simplify block height serialization
* refactor(db): make height serialization length generic
* refactor(db): create a TransactionIndex type
This changes the names of some snapshot types,
but doesn't change any data.
* refactor(db): create transparent OutputIndex and OutputLocation types
This keeps the same serialization, to avoid changing the database version.
* doc(rfc/db): make transparent database type names consistent
* doc(rfc/db): fix a bug in the Utxo.is_coinbase derivation
* fix(db): use the correct serialized size for OutputLocation
* Reject duplicate sprout nullifiers in the state
* Improve docs and error messages
* Clarify "must be present" assert logs
* Move nullifier checks to their own module
Also:
* make non-finalized nullifier checks and errors generic over
sprout, sapling, and orchard
* create and update module and function documentation
* Fix a block type name in docs
* Move state assertions or skip them during tests
These changes enable state testing, while still asserting in production.
* Add sprout duplicate nullifier tests
* Improve comments
* Set value balance to 0 to pass future chain value pool checks
* Test finalized state in sprout nullifier accept test
* Replace assert with expect
* Improve assertion messages
teor