fix(_models): add polymorphic_serialization parameter to model_dump overrides

Pydantic 2.13 added polymorphic_serialization (bool | None) to
model_dump and model_dump_json. The pydantic v1 compat overrides
in _models.py need to match the new signature to satisfy pyright.

Author: musa-cf

src/cloudflare/_models.py

@@ -281,6 +281,7 @@ def model_dump(
             warnings: bool | Literal["none", "warn", "error"] = True,
             fallback: Callable[[Any], Any] | None = None,
             serialize_as_any: bool = False,
+            polymorphic_serialization: bool | None = None,
         ) -> dict[str, Any]:
             """Usage docs: https://docs.pydantic.dev/2.4/concepts/serialization/#modelmodel_dump
 
@@ -353,6 +354,7 @@ def model_dump_json(
             warnings: bool | Literal["none", "warn", "error"] = True,
             fallback: Callable[[Any], Any] | None = None,
             serialize_as_any: bool = False,
+            polymorphic_serialization: bool | None = None,
         ) -> str:
             """Usage docs: https://docs.pydantic.dev/2.4/concepts/serialization/#modelmodel_dump_json