Add Support for Chrono StubTypes

[ThatOneShortGuy]

It seems that the chrono feature from pyo3 isn't supported for the stub gen.

344 |         start_date: NaiveDate,
    |                     ^^^^^^^^^ the trait `PyStubType` is not implemented for `NaiveDate`
    |
    = help: the following other types implement trait `PyStubType`:
              &T
              &str
              ()
              (T1, T2)
              (T1, T2, T3)
              (T1, T2, T3, T4)
              (T1, T2, T3, T4, T5)
              (T1, T2, T3, T4, T5, T6)
            and 57 others

I think it could be added with a feature flag, so it maintains the ergonomics of pyo3.

[ThatOneShortGuy]

I think I've got it figured out, and it works well on my project. I'll leave a PR.