Fix lifetime of TimeSeries in python pyndings

[MaxBetzDLR]

Bug description

A TimeSeries in the memilio-simulation package can be converted into a numpy array. This array is invalid as soon as the referenced Timeseries is invalid. This leads to undefined bahaviour when returning the numpy array from a function.

Version

Any

To reproduce

Steps to reproduce the bug:

1. Create a TimeSeries inside a function, i.e. as result from simulate
2. Create numpy array reference with .as_ndarray()
3. return numpy array from function
4. Leaving scope deletes referenced data and thus numpy array is invalid

Relevant log output

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Checklist

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