Module based e2e test

Add e2e test with session based fixture to test potentially cleanup leaks across different widgets.

An initial draft exist, that was split up but the branch can be used to reimplement e2e tests. (!462) The idea would be to have usage examples for each widget with a session scoped RPCServer and no flushing of the REDIS server in between test. It seems that the e2e fixtures pytest-bec-e2e need to be reviewed in order to be able to remove the --flush-redis, and have session scoped fixtures. This also relates to #497, where we have to better understand whether this is a problem of the async_updates or the pytest-bec-e2e fixtures. However, please also include the observed behavior and Debye where plotting of curves seems to be repeated based on the number of curves added to Waveform (unfortunately this was not yet reproduced in the simulation -> debye_bec#7)