gh-125243: Fix ZoneInfo data race in free threading build (#125281)

Lock `ZoneInfoType` to protect accesses to `ZONEINFO_STRONG_CACHE`.
Refactor the `tp_new` handler to use Argument Clinic so that we can just
use `@critical_section` annotations on the relevant functions.

Also use `PyDict_SetDefaultRef` instead of `PyDict_SetDefault` when
inserting into the `TIMEDELTA_CACHE`.