Backport PR #56114: CLN: Get rid of PyArray_GetCastFunc (#56313)

* Backport PR #56114: CLN: Get rid of PyArray_GetCastFunc

* fix bad indent?

* remove more unintended changes

Author: lithomas1

pandas/_libs/src/vendored/ujson/python/objToJSON.c

@@ -1306,14 +1306,7 @@ char **NpyArr_encodeLabels(PyArrayObject *labels, PyObjectEncoder *enc,
         NPY_DATETIMEUNIT dateUnit = NPY_FR_ns;
         if (PyTypeNum_ISDATETIME(type_num)) {
             is_datetimelike = 1;
-            PyArray_VectorUnaryFunc *castfunc =
-                PyArray_GetCastFunc(PyArray_DescrFromType(type_num), NPY_INT64);
-            if (!castfunc) {
-                PyErr_Format(PyExc_ValueError,
-                             "Cannot cast numpy dtype %d to long",
-                             enc->npyType);
-            }
-            castfunc(dataptr, &i8date, 1, NULL, NULL);
+            i8date = *(npy_int64 *)dataptr;
             dateUnit = get_datetime_metadata_from_dtype(dtype).base;
         } else if (PyDate_Check(item) || PyDelta_Check(item)) {
             is_datetimelike = 1;
@@ -1453,13 +1446,8 @@ void Object_beginTypeContext(JSOBJ _obj, JSONTypeContext *tc) {
 
     if (PyTypeNum_ISDATETIME(enc->npyType)) {
         int64_t longVal;
-        PyArray_VectorUnaryFunc *castfunc =
-            PyArray_GetCastFunc(PyArray_DescrFromType(enc->npyType), NPY_INT64);
-        if (!castfunc) {
-            PyErr_Format(PyExc_ValueError, "Cannot cast numpy dtype %d to long",
-                         enc->npyType);
-        }
-        castfunc(enc->npyValue, &longVal, 1, NULL, NULL);
+
+        longVal = *(npy_int64 *)enc->npyValue;
         if (longVal == get_nat()) {
             tc->type = JT_NULL;
         } else {