chore: cast block number to u64 and not usize #4140

Job	Run time
check	19s
check no_std	22s
clippy	1m 22s
check no_std optimism,kzg-rs	41s
check serde	44s
check std	19s
docs	1m 22s
fmt	5s
test stable --no-default-features	1m 18s
TyposCheck	7s
test stable	1m 22s
test stable --all-features	2m 41s
test beta --no-default-features	57s
test beta	1m 5s
test beta --all-features	1m 41s
test nightly --no-default-features	1m 25s
test nightly	50s
test nightly --all-features	1m 29s
	18m 9s

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