Review block import pipeline for optimization especially with Reth users

[philknows]

@g11tech has reported some Lido CSM users having bad results with timely_target_wrong_head_vote running Lodestar v1.23.x with Reth.

notifyNewPayload roundtrip shows estimated latency around 800ms, which adds to critical time required to see + import the block for head voting, sometimes surpassing the 4s mark.

@nflaig also reports slow notifyNewPayload calls being twice as high as Nethermind at ~150-200ms. Request durations are spiky as well. Importing late head (>4s) seems to correspond with the spikes in duration requests.

Where Nethermind (with comparable hardware) shows:

This ticket is to track the issue and for us to optimize our import block pipeline for max efficiency.