argmin_testfunctions: Edition 2021, approx crate in tests, fixed size input arrays, const generic Rosenbrock derivative and Hessian

[stefan-k]

• It's 2024!
• Set edition 2021 for testfunctions crate
• Use fixed size input arrays for test functions which work only on a fixed number of parameters. Therefore these test functions do not panic anymore.
• Added const generic variants of the Rosenbrock derivative and Hessian. Compared to the non-const variants, those do not allocate.

[codecov-commenter]

Codecov Report

Attention: 46 lines in your changes are missing coverage. Please review.

Comparison is base (a62f6aa) 90.51% compared to head (e588301) 90.39%.

Files	Patch %	Lines
tools/testfunctions/src/rosenbrock.rs	28.81%	42 Missing :warning:
tools/testfunctions/src/sphere.rs	77.77%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #414 +/- ## ========================================== - Coverage 90.51% 90.39% -0.12% ========================================== Files 162 162 Lines 20373 20573 +200 ========================================== + Hits 18440 18597 +157 - Misses 1933 1976 +43 ```

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