Use Cython's array to back Py_ssize_t[::1] (#307)

In `Array`, `Py_ssize_t[::1]` objects are currently backed by [CPython `array`'s]( https://cython.readthedocs.io/en/latest/src/userguide/memoryviews.html#cpython-array-module ) with some internal bits expressed in Cython. However these are not compatible with [Python's Limited API and Stable ABI]( https://docs.python.org/3/c-api/stable.html#c-api-stability ). To address that, switch to [Cython's own `array` type]( https://cython.readthedocs.io/en/latest/src/userguide/memoryviews.html#cython-arrays ). As this is baked into Cython and doesn't use anything special, it is compatible with Python's Limited API and Stable ABI.

xref: rapidsai/build-planning#42

Authors:
  - https://github.com/jakirkham

Approvers:
  - Mads R. B. Kristensen (https://github.com/madsbk)
  - Peter Andreas Entschev (https://github.com/pentschev)

URL: #307

python/ucxx/ucxx/_lib/arr.pyx

@@ -4,13 +4,12 @@
 # cython: language_level=3
 
 
-from cpython.array cimport array, newarrayobject
 from cpython.buffer cimport PyBuffer_IsContiguous
+from cpython.mem cimport PyMem_Free, PyMem_Malloc
 from cpython.memoryview cimport (
     PyMemoryView_FromObject,
     PyMemoryView_GET_BUFFER,
 )
-from cpython.object cimport PyObject
 from cpython.ref cimport Py_INCREF
 from cpython.tuple cimport PyTuple_New, PyTuple_SET_ITEM
 from cython cimport (
@@ -20,6 +19,7 @@ from cython cimport (
     nonecheck,
     wraparound,
 )
+from cython.view cimport array
 from libc.stdint cimport uintptr_t
 from libc.string cimport memcpy
 
@@ -62,13 +62,14 @@ cdef dict itemsize_mapping = {
 }
 
 
-cdef array array_Py_ssize_t = array("q")
+cdef sizeof_Py_ssize_t = sizeof(Py_ssize_t)
 
 
-cdef inline Py_ssize_t[::1] new_Py_ssize_t_array(Py_ssize_t n):
-    return newarrayobject(
-        (<PyObject*>array_Py_ssize_t).ob_type, n, array_Py_ssize_t.ob_descr
-    )
+cdef Py_ssize_t[::1] new_Py_ssize_t_array(Py_ssize_t n):
+    cdef array a = array((n,), sizeof_Py_ssize_t, b"q", "c", False)
+    a.data = <char*>PyMem_Malloc(n * sizeof(Py_ssize_t))
+    a.callback_free_data = PyMem_Free
+    return a
 
 
 @auto_pickle(False)