Resolve deprecation warning about multi-threaded use of fork

[AlanCoding]

You can see the following warning in test output:

tests/integration/test_main.py: 42 warnings
  /usr/lib64/python3.12/multiprocessing/popen_fork.py:66: DeprecationWarning: This process (pid=125488) is multi-threaded, use of fork() may lead to deadlocks in the child.
    self.pid = os.fork()

This is related to a broader python issue, and the default method will actually change in python 3.14.

https://docs.python.org/3/library/multiprocessing.html#contexts-and-start-methods

Note The default start method will change away from fork in Python 3.14. Code that requires fork should explicitly specify that via get_context() or set_start_method().

Anecdotally, there are still a sense of fragility where deadlocks can happen for the subprocesses starting, stopping, and other things. Addressing this issue should go a very long way to establishing stability.

The outcome this issue seeks is that the deprecation warning is addressed.

[AlanCoding]

Follow this for what it will change to python/cpython#84559

• The default ProcessPoolExecutor start method (see
  :ref:multiprocessing-start-methods) changed from fork to forkserver on
  platforms other than macOS & Windows.

If we do go the route of forkserver, we would definitely need to use the .set_forkserver_preload() method, and even this leaves things a little unclear to me as to how we could load everything we really wanted. We also want to check the memory tradeoff involved.