Lock queried rows for each block transaction

[stwiname]

Description

Puts a lock on each query made by handlers in each block.

⚠️ This is untested ⚠️
Things to test:

• It adds the concurrency guarantee we want
• Because we have a transaction for each block, if there are multiple handlers run for the same block that accesses the same value can they still update a single entity multiple times

Motivation

With multichain indexing we need some more concurrency guarantees. We want to prevent the following example from happening.

Chain A reads entity X and then updates it to a new value. Between reading X and updating it chain B updates X.

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• I have tested locally
• I have performed a self review of my changes
• Updated any relevant documentation
• Linked to any relevant issues
• I have added tests relevant to my changes
• Any dependent changes have been merged and published in downstream modules
• My code is up to date with the base branch