Make sure backend.run and Sampler.run can run in a single session

[merav-aharoni]

Summary

Added a test to make sure they run properly.

Details and comments

Fixes #1180

[merav-aharoni]

There was a proposal to issue a warning to let the user know that if backend is run in qiskit_ibm_runtime.Session, then it will actually not be executed in the session (and vice versa). I couldn't find a way to check whether this occurs. Any suggestions?

[coveralls]

Pull Request Test Coverage Report for Build 6868448170

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• 17 of 21 (80.95%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 55.902%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit_ibm_runtime/base_primitive.py	4	5	80.0%
qiskit_ibm_runtime/utils/default_session.py	11	12	91.67%
qiskit_ibm_runtime/ibm_backend.py	1	3	33.33%

Totals
Change from base Build 6856124798:	0.03%
Covered Lines:	2477
Relevant Lines:	4431

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💛 - Coveralls

[kt474]

There was a proposal to issue a warning to let the user know that if backend is run in qiskit_ibm_runtime.Session, then it will actually not be executed in the session (and vice versa). I couldn't find a way to check whether this occurs. Any suggestions?

That's true, I don't see a good way to do this either - maybe we can just write in the docs that this type of behaviour is not supported?

[merav-aharoni]

I added a warning for the case that a Primitive is run within a IBMBackend session. The opposite is not possible, because it creates a circular import.This occurs because Session includes an IBMBackend, so IBMBackend cannot include a Session.

[merav-aharoni]

@kt474 - I think this can be reviewed now. I think a release note is not needed, because it is really part of the backend.run() PR.

[kt474]

LGTM