invalidate indexer block claims

[Theodus]

The gateway's view of a chain is constructed from claims about block { number timestamp hash } claims in the responses of indexers. For simplicity, imagine only 1 indexer serving subgraphs for some chain and imagine the following scenario:

1. indexer responds to some query, including a claim for block info number & hash
2. a following query is sent to the same indexer, using block constraints set to hash
3. the indexer responds with a MissingBlock error for hash

In this situation, the indexer's feedback should overwrite/invalidate its claim for the block it previously provided info for.