DataSet.add_count_dict outcome label mismatch

[sserita]

Describe the bug
Sometime between Sep 2024 and now, there has been a behavior change in DataSet.add_count_dict() that results in the outcome labels being improperly assigned if the first circuit added only has 1 counts.
Edit: Confirmed that 0.9.13 also has this issue, so that narrows our time window down a lot. TBF, I kinda remember touching this function a while ago so this could be my bad.

To Reproduce

Old expected behavior:

New problematic behavior:

Expected behavior
The old behavior is correct.

Environment (please complete the following information):

• pyGSTi pre-0.9.13 to post-0.9.14
• python 3.11
• OSX 15.6

[enielse]

I think I may have encountered this same bug in something related -- will comment more when I have a fix for it.

[enielse]

PR 663 fixes the issue above, and the issue I found. I added the failing code above as a new unit test in test_dataset.py as part of the PR.