benchmarks: save timestamp in json output (#6163)
So that benchmarks run from the same invocation get the same timestamp.
I'm adding timestamps to old JSONL output files with this script:
````
import json
import sys
def replace_timestamps(filename, timestamp):
with open(filename) as read_file:
for line in read_file:
try:
r = json.loads(line.rstrip('\n|\r'))
except json.JSONDecodeError as e:
sys.exit(f'Invalid JSONL:\n{line}{e}')
if 'timestamp' not in r:
r['timestamp'] = float(timestamp)
print(json.dumps(r))
def main():
if len(sys.argv) != 3:
sys.exit("Usage: add_timestamp.py input_file timestamp")
filename = sys.argv[1]
timestamp = sys.argv[2]
replace_timestamps(filename, timestamp)
if __name__ == '__main__':
main()
```
