graphcycles_test: add BM_IsReachableNonConst
graphcycles_test: add BM_IsReachableNonConst

name                          time/op
BM_StressTest/2048             489ns ± 5%
BM_StressTest/4096             501ns ± 6%
BM_StressTest/32768            521ns ± 4%
BM_StressTest/262144           575ns ±11%
BM_StressTest/1048576          614ns ± 2%
BM_ContractEdge/1000           129ns ± 2%
BM_ContractEdge/10000          148ns ± 1%
BM_IsReachableNonConst/10     12.2ns ± 7%
BM_IsReachableNonConst/50     19.9ns ±14%
BM_IsReachableNonConst/100    24.7ns ± 7%
BM_IsReachableNonConst/200    26.3ns ± 3%
BM_IsReachableNonConst/1000   37.3ns ± 5%
BM_IsReachableNonConst/30000  66.4ns ± 3%
