Add `product_ok` and `sum_ok` #628

Job	Run time
check format	13s
msrv	24s
check	12s
test	57s
check (--no-default-features)	13s
check (--no-default-features --features use_alloc)	14s
check (--all-targets --all-features)	24s
All checks succeeded	1s
	2m 38s

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