Client fork grouping does not work for clients that are stuck before the finalization checkpoint

[pk910]

The grouping for the clients fork page does not work properly for clients that are stuck before the finalization checkpoint:

This is happening because dora can't check block relationships for blocks that are older than the finalization checkpoint.
These blocks are no longer in cache, so dora can't iterate their parent tree to group matching fork chains.

#111 is a temporary workaround to group clients that are stuck at the exact same block root.