Add cq support, tracking compression ratio and average bitrate

[SuperCat908809]

Here is my second attempt at implementing the constant quality control parameter to this project. The first is here #70 though its been closed.
In order:

1. Fixed the panic thrown when permutor-cli can't find the VMAF score since the latest ffmpeg has changed how it outputs it.
2. Added the constant quality parameter to permutor-cli. Works for h264_nvenc and hevc_nvenc. Should also work with the other supported codecs though I can't test that.
3. Added compression ratio and average bitrate as a metric that is tracked and displayed during permutor-cli's execution and in its log file. Similar to the FPS metric.

This is my second attempt at this pull request since I didn't realise I was using the wrong github account when I was working on this. I rebased everything with this account as the correct author.

[SuperCat908809]

This should be the fix for Issue: #58
And the implementation of this enhancement: #18

[SuperCat908809]

It seems attempting to rebase my work backfired. I'll have to live with it then.

[Proryanator]

Thank you for opening this PR! I think there are a good amount of overlapping updates like the AV1 PR, so I'll hold off on reviewing this one until that other one is merged in.

That would make this update a lot smaller in scope (already having merged in new changes like the enum, any package updates or other README updates, etc).