gh-136421: Load _datetime static types during interpreter initialization

[ZeroIntensity]

_datetime is a special module, because it's the only non-builtin C extension that contains static types. As such, it would initialize static types in the module's execution function, which can run concurrently. Since static type initialization is not thread-safe, this caused crashes. This fixes it by moving the initialization of _datetime's static types to interpreter startup (where all other static types are initialized), which is already properly protected through other locks.

• Issue: Import _datetime in sub-interpreters in the same time may crash the process #136421