Add doc comments to R__ASSERT/CHECK

[silverweed]

This Pull request:

Adds brief documentation to R__ASSERT and R__CHECK underlining how they do not get stripped in release mode (which might be unexpected for some users). Additionally, it uses R__likely for the check itself, since the condition is expected to be true.

Checklist:

• [x] tested changes locally
• [ ] updated the docs (if necessary)

[github-actions[bot]]

Test Results

    11 files      11 suites   2d 8h 59m 18s :stopwatch:  2 636 tests  2 636 :white_check_mark: 0 :zzz: 0 :x: 27 440 runs  27 440 :white_check_mark: 0 :zzz: 0 :x:

Results for commit b1cdae89.

:recycle: This comment has been updated with latest results.