Specialize `CombinationsWithReplacement::nth` #885

Job	Run time
check	13s
check format	7s
doc	6s
check (--no-default-features)	13s
check (--no-default-features --features use_alloc)	7s
msrv	38s
check (--all-targets --all-features)	17s
semver-checks	18s
test	50s
All checks succeeded	1s
	2m 50s

Provide feedback