Back to fixed window in LED calibration

[GiovanniVolta]

What does the code in this PR do / what does it improve?

We did not identify the reasons for the gain changes with the dynamic window (see here) therefore we are proposing to go back to the fixed window.
The proposed window is [78,142] based on this study.
Note that I did not remove the dynamic window code since I hope we can understand the problem, adjust the code and use it for the future.

Please include the following if applicable:

• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

Notes on testing

• Until the automated tests pass, please mark the PR as a draft.
• On the XENONnT fork we test with database access, on private forks there is no database access for security considerations.

[coveralls]

coverage: 89.514% (+0.03%) from 89.488%
when pulling cd829a0 on back_to_fixed_window
into 7138149 on master.

[dachengx]

Thank you very much @GiovanniVolta !

[GiovanniVolta]

Just to be sure I have checked once more the gain and occupancy with the default plugin, and it looks good