Cleanup: python: Replace 'void' MEM_[cm]allocN with templated, type-safe MEM_[cm]allocN<T>.

The main issue of 'type-less' standard C allocations is that there is no check on
allocated type possible.

This is a serious source of annoyance (and crashes) when making some
low-level structs non-trivial, as tracking down all usages of these
structs in higher-level other structs and their allocation is... really
painful.

MEM_[cm]allocN<T> templates on the other hand do check that the
given type is trivial, at build time (static assert), which makes such issue...
trivial to catch.

NOTE: New code should strive to use MEM_new (i.e. allocation and
construction) as much as possible, even for trivial PoD types.

Pull Request: https://projects.blender.org/blender/blender/pulls/135852

source/blender/python/mathutils/mathutils_interpolate.cc

@@ -65,7 +65,7 @@ static PyObject *M_Interpolate_poly_3d_calc(PyObject * /*self*/, PyObject *args)
   }
 
   if (len) {
-    float *weights = static_cast<float *>(MEM_mallocN(sizeof(float) * len, __func__));
+    float *weights = MEM_malloc_arrayN<float>(size_t(len), __func__);
 
     interp_weights_poly_v3(weights, vecs, len, fp);