Add tests for IMDv2 streams

[ljwoods2]

Is your feature request related to a problem?

No tests currently exist for IMDv2 streams

Describe the solution you'd like

At least some minimal testing that tests some IMDv2 edge cases: frames with only energies, only positions, etc. Also requires a decision on how get_imdsessioninfo will work for v2. Currently I believe its output can change during the stream (if the first frame is only energies for example)- maybe it should just raise a NotImplementedError.

Relate: #75

[orbeckst]

We should test IMDv2 soon, especially if we're advertising that the feature.

Based on the coverage report, https://app.codecov.io/gh/becksteinlab/imdclient/blob/main/imdclient%2FIMDClient.py#L527 none of the IMDv2 functionality is tested.

[orbeckst]

(Remember, untested code is broken code)