Do not reuse event container in source

[maxnoe]

The source reuses the same container for each event, which creates the potential for hard to trace bugs (information from a previous event creeping over into the next) and even uses mutable default arguments (in ctapipe_io_lst.containers) resulting in the exact same containers being used by multiple source instances.

This comes from older versions of ctapipe, where no better solution was available and creating containers was slow, this has improved since a long time though and the same changes have been made in ctapipe.

Sources should not "reuse" containers.