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/duplicate_inputs.cpp

@@ -62,4 +62,4 @@ static void DuplicateInputs(benchmark::Bench& bench)
     });
 }
 
-BENCHMARK(DuplicateInputs);
+BENCHMARK(DuplicateInputs, benchmark::PriorityLevel::HIGH);