feat(engine): track txpool prewarming hit rate

[decofe]

Summary

• retain the transaction hashes represented by each published txpool-prewarm snapshot
• record sync_block_validation_txpool_prewarming_hit_rate during payload validation
• calculate the rate as prewarmed transactions present in the block divided by total block transactions

Testing

• cargo +nightly fmt --check
• cargo check -p reth-engine-tree (blocked: fetching pinned discv5 git dependency returned HTTP 401)

Prompted by: @shekhirin