When env is reset, slack weights are reset too

[BDonnot]

Environment

• Grid2op version: x.y.z (eg 1.4.0)
• lightsim version: x.y.z (eg 0.5.0)
• System: windows, osx, ubuntu16.04, ...
• Additional system information

Note: If the bug concerns an installation issue, you have to provide us with the output of:

python3 setup.py build

AND

pip install -U .

Bug description

How to reproduce

Command line

# command line used if any 

Code snippet

import lightsim2grid

... # Some code 

Current output

The output of the code snippet above

Expected output

The expected output and/or expected behavior description