1429 move example output to example_results

[reneSchm]

Changes and Information

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

• Update implementation of base_dir() and data_dir() (formerly DATA_DIR).
  • Move to io/directories.h.
  • Make both customizable through CMake during configure step.
• Add a new example_results_dir() function, to provide a consistent place for files created by examples.
• Add create_directory_or_exit() as a helper for opening directories (with predictable behavior on errors).
• Use example_results_dir() (and create_directory_or_exit()) to place all files from current examples into example_results/.
• Simplify some examples by using print_table().

If need be, add additional information and what the reviewer should look out for in particular:

Merge Request - Guideline Checklist

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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 within the code (Doxygen) for new functionality has been added in the code.
• Appropriate external documentation (ReadTheDocs) for new functionality has been added to the online documentation and checked in the preview.
• 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).

[codecov]

Codecov Report

❌ Patch coverage is 13.33333% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.31%. Comparing base (20eddb0) to head (9b7977c).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cpp/memilio/io/io.cpp	11.11%	8 Missing ⚠️
cpp/memilio/io/directories.h	16.66%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1544      +/-   ##
==========================================
- Coverage   97.39%   97.31%   -0.08%     
==========================================
  Files         188      188              
  Lines       16621    16634      +13     
==========================================
  Hits        16188    16188              
- Misses        433      446      +13     

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