las3_pub / predictable_parallel_patterns

The current version has race conditions and is hard to debug (especially because of the fibers, if a wrong thread executes on a fiber we get segfalts very fast). To combat this mess we now refactor the code bit by bit while also adding tests where it can be done with reasonably effort).

The rationale to do an custom implementation is that the existing solutions are quite a bit slower and/or require more memory.