[Testing] Add tests for remote features

[Yoric]

The following features rely on pasqal-cloud and don't have tests:

• RemoteEmuMPSExtractor
• RemoteQPUExtractor
• RemoteEmuMPSBackend
• RemoteQPUBackend

Some help setting up a realistic mock server would be invaluable.

Once that is done, we could simply add these extractors/backends to the tests from test_extractors.py (for the extractors) and test_backends.py (for the backends).

Note: there is one example of using the RemoteQPUExtractor in the tutorial 1.