## Problem
Benchmarks run takes about an hour on main branch (in a single job),
which delays pipeline results. And it takes another hour if we want to
restart the job due to some failures.
## Summary of changes
- Use `pytest-split` plugin to run benchmarks on separate CI runners in
4 parallel jobs
- Add `scripts/benchmark_durations.py` for getting benchmark durations
from the database to help `pytest-split` schedule tests more evenly. It
uses p99 for the last 10 days' results (durations).
The current distribution could be better; each worker's durations vary
from 9m to 35m, but this could be improved in consequent PRs.
