(improvement) query, serializers: address PR review feedback

- Replace malloc/free with PyBytes_FromStringAndSize(NULL, ...) pattern in
  vector fast-paths, eliminating extra buffer copy and malloc(0) edge case
- Change _check_int32_range to raise OverflowError instead of struct.error,
  consistent with _check_float_range
- Remove unused imports (struct, malloc, free)
- Differentiate error messages in _raise_bind_serialize_error: 'invalid type'
  for TypeError vs 'value out of range' for OverflowError/struct.error
- Replace unused loop variable with while loop in UNSET_VALUE fill
- Expand __getitem__ docstrings explaining performance rationale
- Fix copyright header in test_parameter_binding.py

Author: mykaul

cassandra/query.py

@@ -489,7 +489,9 @@ def _serializers(self):
 
         The column_encryption_policy check is performed on every access (not
         cached) so that serializers are correctly bypassed if a policy is set
-        after construction.
+        after construction.  This means the cache never goes stale: once a CE
+        policy is present, we always return None and fall through to the
+        encryption-aware bind path.
         """
         if self.column_encryption_policy:
             return None
@@ -573,8 +575,12 @@ def _raise_bind_serialize_error(col_spec, value, exc):
     without wrapping.
     """
     actual_type = type(value)
-    message = ('Received an argument of invalid type for column "%s". '
-               'Expected: %s, Got: %s; (%s)' % (col_spec.name, col_spec.type, actual_type, exc))
+    if isinstance(exc, (OverflowError, struct.error)):
+        reason = 'value out of range'
+    else:
+        reason = 'invalid type'
+    message = ('Received an argument with %s for column "%s". '
+               'Expected: %s, Got: %s; (%s)' % (reason, col_spec.name, col_spec.type, actual_type, exc))
     raise TypeError(message) from exc
 
 
@@ -752,7 +758,7 @@ def bind(self, values):
 
         if proto_version >= 4:
             # Fill remaining unbound columns with UNSET_VALUE (v4+ feature).
-            for i in range(idx, col_meta_len):
+            while idx < col_meta_len:
                 idx = self._append_unset_value(idx)
         elif idx < col_meta_len:
             # Pre-v4: trim trailing unused slots (no UNSET_VALUE support)

tests/unit/test_parameter_binding.py

@@ -1,4 +1,4 @@
-# Copyright DataStax, Inc.
+# Copyright ScyllaDB, Inc.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -326,8 +326,9 @@ def test_cython_path_type_error_wrapped(self):
         assert 'Int32Type' in msg
 
     def test_plain_path_overflow_error_wrapped(self):
-        """Out-of-range int in the plain Python path raises struct.error (caught
-        alongside OverflowError) and is wrapped with column context."""
+        """Out-of-range int in the plain Python path raises OverflowError (from
+        the Cython serializer) or struct.error (from the pure-Python fallback)
+        and is wrapped with column context."""
         column_metadata = [ColumnMetadata('keyspace', 'cf', 'v0', Int32Type)]
         # Force the plain Python path (no Cython serializers)
         prepared = self._make_prepared(column_metadata, serializers=None)