Imports for VECs Can't Happen in Threads

[insertinterestingnamehere]

The following segfaults, but it should work fine:

from threading import Thread
from parla.multiload import multiload_contexts

if __name__ == '__main__':
    def f():
        with multiload_contexts[1]:
            import numpy
    t = Thread(target=f)
    t.start()
    t.join()

[insertinterestingnamehere]

Maybe related? #12

[insertinterestingnamehere]

Probably also related: #12

[insertinterestingnamehere]

Trace for this one:

0x7ff912225188: (handler+0x28)
0x7ff91252a830: (killpg+0x40)
0x7ff903cc7ece: (parse_iso_8601_datetime+0x44e)
0x100000001: -- error: unable to obtain symbol name for this frame

This points to https://github.com/numpy/numpy/blob/623bc1fae1d47df24e7f1e29321d0c0ba2771ce0/numpy/core/src/multiarray/datetime_strings.c#L221 as the issue. Offhand, I have no idea why that would be an issue though.