internal: Add a `fastpickle` module to help with multiprocess serialization. Looks like we're wasting a lot of time serializing custom class information for the workers, so this new module helps to convert classes to standard structures (dicts, lists, etc).

import os


def slashfix(path):
    if path is None:
        return None
    if isinstance(path, str):
        return path.replace('/', os.sep)
    fixed = []
    for p in path:
        fixed.append(p.replace('/', os.sep))
    return fixed