Rewrite `MultiProduct` #728

Job	Run time
doc	18s
check format	7s
check	18s
check (--no-default-features)	7s
check (--no-default-features --features use_alloc)	8s
msrv	45s
semver-checks	34s
check (--all-targets --all-features)	18s
test	56s
All checks succeeded	1s
	3m 32s

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