gh-71587: Establish global state in `_datetime` (#110475)

* Use explicit initialiser for m_base
* Add module state stub; establish global state on stack
* Put conversion factors in state struct
* Move PyDateTime_TimeZone_UTC to state
* Move PyDateTime_Epoch to state struct
* Fix ref leaks in and clean up initialisation

Erlend E. Aasland committed 2y ago

ec5622d1977c03960883547f7b8f55c26ac85df2

Parent: ea530f2

Committed by GitHub <noreply@github.com> on 10/12/2023, 8:28:10 AM