refactor: remove `Integraal::compute_error`

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 94.66%. Comparing base (f405c5f) to head (e5532f2). Report is 2 commits behind head on trunk.

Files	Patch %	Lines
integraal/src/structure/tests.rs	85.71%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## trunk #28 +/- ## ========================================== + Coverage 92.96% 94.66% +1.70% ========================================== Files 3 3 Lines 341 281 -60 ========================================== - Hits 317 266 -51 + Misses 24 15 -9 ```

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