Fixed issue with --diff-branch arg in dynamo benchmarks (#93989)
As @peterbell10 pointed out, it was giving incorrect results for `compression_ratio`
and `compression_latency` when you used `--diff-branch`.
This fixes this by running a separate subprocess for each branch to make sure you are not being affected by run for other branch.
Also added a couple of more significant figures
to numbers in summary table.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/93989
Approved by: https://github.com/jansel
