Specialize `CombinationsWithReplacement::nth` #882

Job	Run time
msrv	47s
check format	8s
doc	16s
check	15s
semver-checks	2m 25s
check (--no-default-features)	17s
test	49s
check (--no-default-features --features use_alloc)	9s
check (--all-targets --all-features)	24s
All checks succeeded	1s
	5m 31s

Provide feedback