Address review feedback: harden numpy_parser and improve tests

- Add buffer size guard before memcpy in unpack_row() to prevent overflow
- Remove dead mask_true constant and unused uint8_t cimport
- Fix copyright header (DataStax -> ScyllaDB)
- Replace hard-coded little-endian dtypes with native numpy dtypes
- Remove unused Mock import
- Add test for NULL vector mask handling
- Add test for unsupported subtype fallback to object array

Author: mykaul

cassandra/numpy_parser.pyx

@@ -25,7 +25,7 @@ as numpy is an optional dependency.
 include "ioutils.pyx"
 
 cimport cython
-from libc.stdint cimport uint64_t, uint8_t
+from libc.stdint cimport uint64_t
 from libc.string cimport memset
 from cpython.ref cimport Py_INCREF, PyObject
 
@@ -74,8 +74,6 @@ _cqltype_to_numpy = {
 
 obj_dtype = np.dtype('O')
 
-cdef uint8_t mask_true = 0x01
-
 cdef class NumpyParser(ColumnParser):
     """Decode a ResultMessage into a bunch of NumPy arrays"""
 
@@ -181,6 +179,10 @@ cdef inline int unpack_row(
             Py_INCREF(val)
             (<PyObject **> arr.buf_ptr)[0] = <PyObject *> val
         elif buf.size >= 0:
+            if buf.size > arr.stride:
+                raise ValueError(
+                    "Column %d: received %d bytes but array stride is %d" %
+                    (i, buf.size, arr.stride))
             memcpy(<char *> arr.buf_ptr, buf.ptr, buf.size)
         else:
             memset(<char *>arr.mask_ptr, 1, arr.mask_stride)