Specialize `Interleave[Shortest]::fold` #707

Job	Run time
doc	15s
check	10s
check format	6s
check (--no-default-features)	8s
msrv	39s
check (--no-default-features --features use_alloc)	10s
test	53s
check (--all-targets --all-features)	18s
All checks succeeded	1s
	2m 40s

Provide feedback