feat: add epsilon computation to the main structure

[imrn99]

Summary

Add a new method to the main structure: Integraal::compute_error. This method computes the error one can expect from the approximation of the integral. Note that the value should be taken with a grain of salt since there is some derivative approximation involved.

Content

• Scope:
  • [x] Code
• Type of change:
  • [x] New feature(s)
• Necessary follow-up:
  • [x] Needs testing: test should make use of this to adjust their tolerance

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 49 lines in your changes are missing coverage. Please review.

Project coverage is 78.04%. Comparing base (94392e5) to head (3ae9258).

Files	Patch %	Lines
integraal/src/structure/implementations.rs	0.00%	49 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## trunk #15 +/- ## =========================================== - Coverage 93.52% 78.04% -15.49% =========================================== Files 3 3 Lines 247 296 +49 =========================================== Hits 231 231 - Misses 16 65 +49 ```

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