* Add round-trip test for OutputLocation disk serialization
* Make the transaction snapshot tests more accurate
Previously, we were showing the genesis transaction hash at height 0, index 0.
But its hash is actually not stored by location in the database,
because the genesis transaction is skipped due to a consensus rule.
* Update the transaction snapshot data
* Add history tree snapshot tests
At the current test heights, the history trees are all empty.
* Add the history tree snapshot data
* Update comments
* Simplify snapshot test code
* Make some serde::Serialize impls test-only, so we can hex-encode them
This should also speed up release compilation a bit.
* Add snapshot test code for UTXOs
* Add snapshot data for UTXOs
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