Logger doesn't support weak reference

[pamelafox]

CPython Logger supports weak reference, picologging Logger does not.

Supporting weakreference is fairly straightforward:
https://docs.python.org/3.10/extending/newtypes.html#weak-reference-support

I tested that change locally and it works. I haven't been able to ascertain how much of a performance hit it is (if any), however. Let me know what you think and whether you'd like a PR.

[pamelafox]

I actually have this branch locally but wasn't sure if it was desired, as I read it might introduce a slight performance hit. @tonybaloney Is it worth adding?