[Fuzzing] Use random.randbytes in fuzz_opt.py (#9332)

make_random_input() previously generated random bytes using a Python
list comprehension calling random.randint(0, 255) up to 200,000 times
per input file (~18.5ms average per call). Replace this loop with
random.randbytes(input_size) (~0.3ms average per call, ~50x faster).

Steady-state throughput increases by +7.8% (3.08 -> 3.32 iters/s) for a
single worker and +7.4% (81.78 -> 87.85 iters/s) across 32 parallel
workers.

Author: tlively

scripts/fuzz_opt.py

@@ -114,7 +114,7 @@ def random_size():
 
 def make_random_input(input_size, raw_input_data):
     with open(raw_input_data, 'wb') as f:
-        f.write(bytes([random.randint(0, 255) for x in range(input_size)]))
+        f.write(random.randbytes(input_size))
 
 
 def run(cmd, stderr=None, silent=False):