REF: Avoid np.can_cast for scalar inference for NEP 50 (#55707)

* REF: Avoid np.can_cast for scalar inference for NEP 50

* Use helper function

* end->stop

* ignore typing

* Address NEP 50 later

ci/run_tests.sh

@@ -10,7 +10,8 @@ echo PYTHONHASHSEED=$PYTHONHASHSEED
 
 COVERAGE="-s --cov=pandas --cov-report=xml --cov-append --cov-config=pyproject.toml"
 
-PYTEST_CMD="MESONPY_EDITABLE_VERBOSE=1 PYTHONDEVMODE=1 PYTHONWARNDEFAULTENCODING=1 pytest -r fEs -n $PYTEST_WORKERS --dist=loadfile $TEST_ARGS $COVERAGE $PYTEST_TARGET"
+# TODO: Support NEP 50 and remove NPY_PROMOTION_STATE
+PYTEST_CMD="NPY_PROMOTION_STATE=legacy MESONPY_EDITABLE_VERBOSE=1 PYTHONDEVMODE=1 PYTHONWARNDEFAULTENCODING=1 pytest -r fEs -n $PYTEST_WORKERS --dist=loadfile $TEST_ARGS $COVERAGE $PYTEST_TARGET"
 
 if [[ "$PATTERN" ]]; then
   PYTEST_CMD="$PYTEST_CMD -m \"$PATTERN\""

pandas/core/dtypes/cast.py

@@ -699,7 +699,7 @@ def _maybe_promote(dtype: np.dtype, fill_value=np.nan):
             dtype = np.dtype(np.object_)
 
         elif issubclass(dtype.type, np.integer):
-            if not np.can_cast(fill_value, dtype):
+            if not np_can_cast_scalar(fill_value, dtype):  # type: ignore[arg-type]
                 # upcast to prevent overflow
                 mst = np.min_scalar_type(fill_value)
                 dtype = np.promote_types(dtype, mst)
@@ -1916,4 +1916,25 @@ def _dtype_can_hold_range(rng: range, dtype: np.dtype) -> bool:
     """
     if not len(rng):
         return True
-    return np.can_cast(rng[0], dtype) and np.can_cast(rng[-1], dtype)
+    return np_can_cast_scalar(rng.start, dtype) and np_can_cast_scalar(rng.stop, dtype)
+
+
+def np_can_cast_scalar(element: Scalar, dtype: np.dtype) -> bool:
+    """
+    np.can_cast pandas-equivalent for pre 2-0 behavior that allowed scalar
+    inference
+
+    Parameters
+    ----------
+    element : Scalar
+    dtype : np.dtype
+
+    Returns
+    -------
+    bool
+    """
+    try:
+        np_can_hold_element(dtype, element)
+        return True
+    except (LossySetitemError, NotImplementedError):
+        return False