Implement a `Base.show` for `OptimizationStats`

[nathanaelbosch]

DEStats are nicely presented in the REPL. This PR implements the same functionality for OptimizationStats.

Checklist

• [ ] Appropriate tests were added
• [ ] Any code changes were done in a way that does not break public API
• [ ] All documentation related to code changes were updated
• [ ] The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• [x] Any new documentation only uses public API

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 38.43%. Comparing base (9cd4382) to head (4ba2869).

Files	Patch %	Lines
src/solutions/optimization_solutions.jl	0.00%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #652 +/- ## ========================================== - Coverage 38.49% 38.43% -0.07% ========================================== Files 55 55 Lines 4291 4298 +7 ========================================== Hits 1652 1652 - Misses 2639 2646 +7 ```

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