Include AR metrics in COCOEvaluator results

[carandraug]

This PR adds AR metrics to the results of COCOEvaluator. This was requested on the discussion of issue #1296 to which the reply was to submit a PR:

Originally posted by @ppwwyyxx in #1296 (comment):

does not contain the AR,

AR is not commonly used, and is therefore not included in results. You can send a PR to add it.

or any of the stats from above the line "Evaluation results for bbox".

everything except for AR are included.

Here's that PR.

I split this into two commits. The first commit adds the "global" AR metrics only (effectively the value displayed by COCOEval.summarize()). The second commit adds the per-class AR.

[carandraug]

The failed checks appear to be due to some issues with the CI configuration (indeed the last pushed commit that passed all the checks was 9 months ago)