test

Implements parallel leaf hashing in `process_sorted_pairs_to_leaves` #18

Job	Run time
test stable on ubuntu with default	3m 50s
test stable on ubuntu with smt-hashmaps	3m 48s
test stable on ubuntu with no-std	3m 40s
test nightly on ubuntu with default	3m 48s
test nightly on ubuntu with smt-hashmaps	3m 51s
test nightly on ubuntu with no-std	3m 31s
	22m 28s

Provide feedback