LAr AC classifier: changes to `larveto.py`

[rosannadeckert]

• [x] split time term from amplitude term & added correct signs (minus for time term, plus for amplitude)
• [x] made time pdf a true normalized pdf by adding (1-bkg_prob) factor in front of double exponential
• [x] changed naming sing2trip_ratio -> sing2tot_ratio
• [x] changed amplitude pdf to log pdf to mitigate numerical problems
• [x] amplitude log pdf function uses user-provided pdf (and arg in the main function)
• [x] review numerical stability
• [x] allow for changing the probability of random pulses (and arg in the main function)
• [x] filter pulses with a noise threshold suitable for the classifier (i.e. no afterpulses)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 21.38%. Comparing base (e7b7b36) to head (6a4ce89). Report is 223 commits behind head on main.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #574 +/- ## ========================================== + Coverage 21.34% 21.38% +0.03% ========================================== Files 42 42 Lines 7907 7907 ========================================== + Hits 1688 1691 +3 + Misses 6219 6216 -3 ```

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