305 add ccache to linux build

[dabele]

Changes and Information

• added ccache to CI linux builds (other builds maybe added later after some observation)
• simplified linux build options, removed unused options to make the cache key easier

To see that the cache is working correctly:

• The ccache action reports loading the cache at the beginning of the build job and cache misses/hits at the end
• stored cache files can be viewed in github -> actions -> caches; this development branch doesn't save caches anymore but there are some cache files around from my testing
• I tested the cache on the development branch before I added the restriction to only save on the main branch. compile times went down from ~15 mins to ~5 mins. this is with identical code, i.e. 100% cache hits. Compile times should be checked after a few nightly builds to see if everything works there.

Closes #305

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

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

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.23%. Comparing base (575a146) to head (5c47821). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #994 +/- ## ======================================= Coverage 96.23% 96.23% ======================================= Files 128 128 Lines 10852 10852 ======================================= Hits 10443 10443 Misses 409 409 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[mknaranja]

@dabele Who has been involved here and who is supposed to do the review?

[dabele]

@dabele Who has been involved here and who is supposed to do the review?

it's not done yet. but I need the CI to run for testing this, so it's not a draft.

[dabele]

A little off topic, but does this already help with the boost dependency, or do we need another solution for that? It currently takes up a lot of CI time, both for the download itself as well as for packing and transferring artifacts, as these pack the entire build directory.

Sadly, this doesn't help with that. I though about caching boost, but this would only be possible if the same bootstrapped boost is usable by all builds (or at least all builds of the same operating system family). boost is more than 1G, so if every build needs it's own cached version this will exceed the limit. This will only help with the download and bootstrap phase of boost, not sure what could be done about the artifact size. I guess only saving artifacts that are really required, i.e. test executables and shared objects.