refactor: type physical_optimizer_rules with an Exportable Protocol

Replace the `list[Any]` hint on the SessionContext `physical_optimizer_rules` argument with a `PhysicalOptimizerRuleExportable` Protocol, matching the existing `TableProviderExportable` / `*Exportable` pattern used for other FFI-capsule objects.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: timsaucer

python/datafusion/context.py

@@ -130,6 +130,16 @@ class TableProviderExportable(Protocol):
     def __datafusion_table_provider__(self, session: Any) -> object: ...  # noqa: D105
 
 
+class PhysicalOptimizerRuleExportable(Protocol):
+    """Type hint for object that has __datafusion_physical_optimizer_rule__ PyCapsule.
+
+    The capsule wraps an ``FFI_PhysicalOptimizerRule``, typically produced by a
+    separate compiled extension.
+    """
+
+    def __datafusion_physical_optimizer_rule__(self) -> object: ...  # noqa: D105
+
+
 class SessionConfig:
     """Session configuration options."""
 
@@ -524,7 +534,7 @@ def __init__(
         self,
         config: SessionConfig | None = None,
         runtime: RuntimeEnvBuilder | None = None,
-        physical_optimizer_rules: list[Any] | None = None,
+        physical_optimizer_rules: list[PhysicalOptimizerRuleExportable] | None = None,
     ) -> None:
         """Main interface for executing queries with DataFusion.