feat: reapply to_plain_state (#1778) #4470

Job	Run time
docs	1m 26s
clippy	1m 31s
check	25s
check no_std	21s
check serde	26s
check no_std optimism,kzg-rs	40s
fmt	16s
check std	27s
test stable --no-default-features	58s
test stable	1m 4s
TyposCheck	6s
test stable --all-features	1m 38s
test beta --no-default-features	55s
test beta	1m 21s
test beta --all-features	1m 38s
test nightly --no-default-features	55s
test nightly	53s
test nightly --all-features	1m 23s
	16m 23s

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