Adjust Optimism (Mainnet) `TotalDifficulty` calculation #9781

Job	Run time
Build (release, Nethermind)	2m 4s
Build (release, EthereumTests)	1m 20s
Build (release, Benchmarks)	1m 0s
Build (debug, Nethermind)	1m 56s
Build (debug, EthereumTests)	1m 23s
Build (debug, Benchmarks)	1m 8s
	8m 51s

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