bench: explicitly make all current benchmarks "high" priority

no-functional changes. Only have set the priority level explicitly
on every BENCHMARK macro call.

src/bench/rollingbloom.cpp

@@ -32,5 +32,5 @@ static void RollingBloomReset(benchmark::Bench& bench)
     });
 }
 
-BENCHMARK(RollingBloom);
-BENCHMARK(RollingBloomReset);
+BENCHMARK(RollingBloom, benchmark::PriorityLevel::HIGH);
+BENCHMARK(RollingBloomReset, benchmark::PriorityLevel::HIGH);