Weird stall when running tests on Mac with M1 processor

[vlad0x00]

• When running tests on Mac with M1, the helper process stalls at https://github.com/bcgsc/btllib/blob/master/include/btllib/process_pipeline.hpp#L681
  Specifically, calling the pipeline_map() function which returns a global variable stalls. This is somewhat bizare, as it's a very straightforward function. The function itself is a bit of a hack, though, but is necessary as defining global variables is impossible in a standard way in a header-only library. This might be fixed by transitioning to a compiled library.
• This seems to only happen when running tests in Meson, but not when an independent binary is compiled with btllib.