Fix also _Py_InitializeEx_Private(): initialize time before initializing
import, import_init() uses the _PyTime API (for thread locks).

_PyTime_AsMicroseconds() rounding.

Add also unit tests.

using the C volatile keyword.

Use _PyTime_ROUND_FLOOR and _PyTime_ROUND_CEILING instead.

Add also more tests for ROUNd_FLOOR.

check that microseconds and nanoseconds fits into the specified range.

Add _PyTime_AsTimeval_noraise() function. Call it when it's not possible (or
not useful) to raise a Python exception on overflow.

- _PyTime_ObjectToTime_t()
- _PyTime_ObjectToTimespec()
- _PyTime_ObjectToTimeval()