Fix for amplitude_bell size offset

[arrrrrmin]

As promised in https://github.com/TimeEval/GutenTAG/issues/49 here is the fix for the amplitude_bell size offset (fixes #49). I’m not very familiar with unittest TestCase-Classes, @CodeLionX could you please review the tests/test_generator/test_lengths.py? There might be a more efficient way to check for the valid generation of anomalies under different length values?

Greetings and thanks for the very fast reply.

[codecov[bot]]

Codecov Report

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

Project coverage is 90.00%. Comparing base (b2b18ca) to head (3697c3c).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #50 +/- ## ========================================== + Coverage 89.99% 90.00% +0.01% ========================================== Files 53 53 Lines 2088 2091 +3 ========================================== + Hits 1879 1882 +3 Misses 209 209 ``` | [Flag](https://app.codecov.io/gh/TimeEval/GutenTAG/pull/50/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TimeEval) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/TimeEval/GutenTAG/pull/50/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TimeEval) | `90.00% <100.00%> (+0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=TimeEval#carryforward-flags-in-the-pull-request-comment) to find out more.

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[CodeLionX]

Mypy still fails on the test-file. You can add # type: ignore to the corresponding lines because specifying the full correct type of the config object is too verbose.