fix(test_interpolate): ensure interpolation nodes generally not becoming too small around zero

[codecov-commenter]

Codecov Report

Base: 77.25% // Head: 77.20% // Decreases project coverage by -0.04% :warning:

Coverage data is based on head (e6cc001) compared to base (6263325). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #300 +/- ## ========================================== - Coverage 77.25% 77.20% -0.05% ========================================== Files 29 29 Lines 2242 2242 Branches 366 366 ========================================== - Hits 1732 1731 -1 Misses 382 382 - Partials 128 129 +1 ``` | [Impacted Files](https://codecov.io/gh/PTB-M4D/PyDynamic/pull/300?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PTB-M4D) | Coverage Δ | | |---|---|---| | [src/PyDynamic/model\_estimation/fit\_filter.py](https://codecov.io/gh/PTB-M4D/PyDynamic/pull/300/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PTB-M4D#diff-c3JjL1B5RHluYW1pYy9tb2RlbF9lc3RpbWF0aW9uL2ZpdF9maWx0ZXIucHk=) | `89.96% <0.00%> (-0.34%)` | :arrow_down: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PTB-M4D). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=PTB-M4D)

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