Fix jq load_probabilities precision error using python

[zifeishan]

jq has a precision bug while loading probabilities with big vids, due to a known issue that it's using double floating numbers to store integers. There seems no good way in jq to support better precision: https://github.com/stedolan/jq/issues/369

We've tried using awk with --bignum but versioning seems a problem.

Here we just try to use python3 to do the job.