fix: use statement.copy() to avoid protected attribute access

Fixes pyright reportPrivateUsage error by using the public copy() API
instead of directly accessing _named_parameters and _positional_parameters.

Author: cofin

sqlspec/driver/_common.py

@@ -1363,12 +1363,9 @@ def _get_compiled_statement(
         if params is not None and not isinstance(params, (list, tuple, dict)):
             try:
                 materialized = list(params)
-                # Update the statement's internal parameters with materialized values
-                if statement._named_parameters:
-                    # Named parameters are stored as dict, shouldn't be an iterator
-                    pass
-                else:
-                    statement._positional_parameters = materialized
+                # Create a copy of the statement with materialized parameters
+                # to avoid consuming the iterator during cache key generation
+                statement = statement.copy(parameters=materialized)
             except TypeError:
                 pass  # Not iterable, proceed normally