Add/reorganize scalar Timedelta tests

pandas/_libs/ops.pxd

@@ -0,0 +1,5 @@
+from numpy cimport int64_t
+
+
+cpdef int64_t calc_int_int(object op, int64_t a, int64_t b) except? -1
+cpdef int64_t calc_int_float(object op, int64_t a, double b) except? -1

pandas/_libs/ops.pyi

@@ -48,3 +48,5 @@ def maybe_convert_bool(
     *,
     convert_to_masked_nullable: Literal[True],
 ) -> tuple[np.ndarray, np.ndarray]: ...
+def calc_int_int(op, left: int, right: int) -> int: ...
+def calc_int_float(op, left: int, right: float) -> int: ...

pandas/_libs/ops.pyx

@@ -16,6 +16,7 @@ import numpy as np
 
 from numpy cimport (
     import_array,
+    int64_t,
     ndarray,
     uint8_t,
 )
@@ -308,3 +309,20 @@ def maybe_convert_bool(ndarray[object] arr,
             return (arr, None)
     else:
         return (result.view(np.bool_), None)
+
+
+@cython.overflowcheck(True)
+cpdef int64_t calc_int_int(object op, int64_t a, int64_t b) except? -1:
+    """
+    Calculate op(a, b) and return the result. Raises OverflowError if converting either
+    operand or the result to an int64_t would overflow.
+    """
+    return op(a, b)
+
+@cython.overflowcheck(True)
+cpdef int64_t calc_int_float(object op, int64_t a, double b) except? -1:
+    """
+    Calculate op(a, b) and return the result. Raises OverflowError if converting either
+    operand or the result would overflow.
+    """
+    return op(a, b)