Add background stateless block processing task to collect state diffs

[tanishqjasoria]

Nethermind client is capable of stateless block processing post verkle. This means that we can conitune to process block even while we are in the sync mode. This is very importatant for verkle sync as we use the ExecutionWitness to assist with the healing phase - We execute the block and get the modified values and use that to heal the state tree.

We already have post-state values in the block but there is no way to verify those values without actually executing the block and we dont want to use values that are not verified.

So, we need a background task that can keep processing block when the node is in sync mode and verify/update the post-state values.