✅ Add type tests covering all relevant datetime64 and timedelta64 (#859)

* add type tests covering all relevant datetime64 and timedelta64

* tests: ignore assert_type errors

* add comment for type ignores

* Update src/numpy-stubs/@test/static/accept/temporal_scalar_ops.pyi

Author: Aniketsy

src/numpy-stubs/@test/static/accept/temporal_scalar_ops.pyi

@@ -0,0 +1,73 @@
+# Type tests for datetime64/timedelta64 operations using representative subtype cases
+
+import datetime as dt
+from typing import assert_type
+
+import numpy as np
+
+DT = np.datetime64
+TD = np.timedelta64
+
+dt_default: DT
+dt_none: DT[None]
+dt_int: DT[int]
+dt_datetime: DT[dt.datetime]
+dt_date: DT[dt.date]
+
+td_default: TD
+td_none: TD[None]
+td_int: TD[int]
+td_timedelta: TD[dt.timedelta]
+
+assert_type(dt_default + td_default, DT)
+assert_type(dt_default + td_none, DT[None])
+# mypy incorrectly infers this as "timedelta64[Any]" but pyright behaves correctly
+assert_type(dt_none + td_default, DT[None])  # type: ignore[assert-type]
+assert_type(dt_int + td_int, DT[int])
+assert_type(dt_datetime + td_timedelta, DT[dt.datetime])
+assert_type(dt_date + td_timedelta, DT[dt.date])
+
+assert_type(dt_default - td_default, DT)
+assert_type(dt_default - td_none, DT[None])
+assert_type(dt_none - td_default, DT[None])  # type: ignore[assert-type]
+assert_type(dt_int - td_int, DT[int])
+assert_type(dt_datetime - td_timedelta, DT[dt.datetime])
+assert_type(dt_date - td_timedelta, DT[dt.date])
+assert_type(dt_date - td_int, DT[dt.date | int])
+
+assert_type(dt_default - dt_default, TD)
+assert_type(dt_none - dt_default, TD[None])  # type: ignore[assert-type]
+assert_type(dt_int - dt_int, TD[int])
+assert_type(dt_datetime - dt_datetime, TD[dt.timedelta])
+assert_type(dt_date - dt_date, TD[dt.timedelta])
+
+assert_type(td_default + td_default, TD)
+assert_type(td_none + td_default, TD[None])  # type: ignore[assert-type]
+assert_type(td_int + td_int, TD[int])
+assert_type(td_timedelta + td_timedelta, TD[dt.timedelta])
+
+assert_type(td_default - td_default, TD)
+assert_type(td_none - td_default, TD[None])  # type: ignore[assert-type]
+assert_type(td_int - td_int, TD[int])
+assert_type(td_timedelta - td_timedelta, TD[dt.timedelta])
+
+assert_type(td_default / td_default, np.float64)
+assert_type(td_none / td_default, np.float64)
+
+assert_type(td_default % td_default, TD)
+assert_type(td_none % td_default, TD[None])  # type: ignore[assert-type]
+
+assert_type(td_default * 0, TD)
+assert_type(td_none * 0, TD[None])
+assert_type(td_int * 0, TD[int])
+assert_type(td_timedelta * 0, TD[dt.timedelta])
+
+assert_type(0 * td_default, TD)
+assert_type(0 * td_none, TD[None])
+assert_type(0 * td_int, TD[int])
+assert_type(0 * td_timedelta, TD[dt.timedelta])
+
+assert_type(td_default / 0, TD)
+assert_type(td_none / 0, TD[None])
+assert_type(td_int / 0, TD[int])
+assert_type(td_timedelta / 0, TD[dt.timedelta])