L2: Consider delaying the watcher to a few blocks back.

[fkrause98]

Description

Ethereum has re-orgs and soft-forks (ommer blocks) frequently enough that we should consider it
something to be handled. This brings the issue that our watcher could believe that a wrong block has
the source of truth.

Solution

Make the watcher only consider blocks from a couple of numbers below the current eth_blockNumber.
My suggestion? 2 epochs should be enough ( 1 epoch = 32 blocks in mainnet). But we can discuss it before.