Bug in Windows with multiprocessing

Hi. I ran into an issue when using tomlkit on windows with multiprocessing.

import multiprocessing as mp
import tomlkit


class Worker: 
    def run(self): 
        print(self.db_conf) 
        print(self.db_conf['path'])
        # bug here, get() returns None
        print(self.db_conf.get('path')) 

if __name__ == '__main__':
    w = Worker()
    conf = tomlkit.loads("""
    [db]
    path = '~/files/'
    """)
    w.db_conf = conf['db']
    p = mp.Process(target=w.run)
    p.start()
    p.join()

The output is:

{'path': '~/files/'}
~/files/
None

Somehow Container.get() lost track of the values after pickling into another process. On Linux this script works fine.

Start with the supplied Windows multiprocessing reproducer and inspect tomlkit's Container.get() behavior when the container is pickled into another process. Compare direct indexing with get('path') before and after process transfer, and compare Windows with Linux if available. Done means the reproduced configuration lookup behaves consistently across processes.