PLT-8339: Fix SQL instances for ChainPoint and ChainTip

[ana-pantilie]

Both ChainPoint and ChainTip can refer to the genesis block, in this case they don't carry any data. This should be reflected in the SQL representation correctly, therefore we need to make the changes in this PR.

@berewt pointed out the tests in

marconi/marconi-chain-index/test/Spec/Marconi/ChainIndex/Orphans.hs

Line 103 in 830f9ea

propSQLFieldRoundtripBlockHeaderHash :: Property

, unfortunately I wasn't able to write similar ones for these changes. The reason is that these would be tests for the RowParser, and the SQL package we use doesn't seem to have a way to run this parser in a pure context. I am 100% open to suggestions, let me know if there's something I'm missing here!

Also, there doesn't seem to be a way to return errors from the RowParser context, so I had to throw exceptions. Please let me know if we need to do something else here.

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[berewt]

LGTM.
It's ok to throw errors, we catch them anyway https://github.com/input-output-hk/marconi/blob/main/marconi-core/src/Marconi/Core/Indexer/SQLiteIndexer.hs#L213-L220
We could maybe unwrap the RowParser using an internal module, but we can skip it at the moment.