bpo-46417: time module uses PyStructSequence_NewType() (GH-30734)

bpo-46417: time module uses PyStructSequence_NewType() (GH-30734)

The time module now creates its struct_time type as a heap
type using PyStructSequence_NewType(), rather than using a static
type.

* Add a module state to the time module: add traverse, clear and free
  functions.
* Use PyModule_AddType().
* Remove the 'initialized' variable.