fix: add @overload to Engine.render_python_module for correct mypy typing

When archive_name is a str, the method returns tuple[ModuleType, Any].
When archive_name is None (default), it returns just ModuleType.
Without overloads, mypy sees the union return type and rejects tuple
unpacking at call sites (attr-defined: Module has no __iter__).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: VeaaC

flatdata-generator/flatdata/generator/engine.py

@@ -4,7 +4,7 @@
 '''
 
 import types
-from typing import Any
+from typing import Any, overload
 
 from flatdata.generator.tree.builder import build_ast
 from flatdata.generator.tree.nodes.trivial.namespace import Namespace
@@ -65,6 +65,11 @@ def render(self, generator_name: str) -> str:
         output_content = generator.render(self.tree)
         return str(output_content)
 
+    @overload
+    def render_python_module(self, module_name: str | None = None, *, archive_name: str, root_namespace: str | None = None) -> tuple[types.ModuleType, Any]: ...
+    @overload
+    def render_python_module(self, module_name: str | None = None, archive_name: None = None, root_namespace: str | None = None) -> types.ModuleType: ...
+
     def render_python_module(self, module_name: str | None = None, archive_name: str | None = None, root_namespace: str | None = None) -> types.ModuleType | tuple[types.ModuleType, Any]:
         """
         Render python module.