Explicit stepper wrapper

[reneSchm]

Changes and Information

Please briefly list the changes (main added features, changed items, or corrected bugs) made:

• Add ExplicitStepperWrapper class. Allows using non-adaptive explicit steppers from boost.
• Extend Euler integration test for new steppers.

Merge Request - Guideline Checklist

Please check our git workflow. Use the draft feature if the Pull Request is not yet ready to review.

Checks by code author

• Every addressed issue is linked (use the "Closes #ISSUE" keyword below)
• New code adheres to coding guidelines
• No large data files have been added (files should in sum not exceed 100 KB, avoid PDFs, Word docs, etc.)
• Tests are added for new functionality and a local test run was successful (with and without OpenMP)
• Appropriate documentation for new functionality has been added (Doxygen in the code and Markdown files if necessary)
• Proper attention to licenses, especially no new third-party software with conflicting license has been added
• (For ABM development) Checked benchmark results and ran and posted a local test above from before and after development to ensure performance is monitored.

Checks by code reviewer(s)

• Corresponding issue(s) is/are linked and addressed
• Code is clean of development artifacts (no deactivated or commented code lines, no debugging printouts, etc.)
• Appropriate unit tests have been added, CI passes, code coverage and performance is acceptable (did not decrease)
• No large data files added in the whole history of commits(files should in sum not exceed 100 KB, avoid PDFs, Word docs, etc.)
• On merge, add 2-5 lines with the changes (main added features, changed items, or corrected bugs) to the merge-commit-message. This can be taken from the briefly-list-the-changes above (best case) or the separate commit messages (worst case).

[HenrZu]

Looks very nice and is a nice addition :) Just commented on a few little things about the documentation.