Add wpistruct typing utilities

subprojects/robotpy-wpiutil/wpiutil/wpistruct/typing.py

@@ -0,0 +1,23 @@
+from typing import ClassVar, Protocol
+
+try:
+    from typing import TypeGuard
+except ImportError:
+    try:
+        from typing_extensions import TypeGuard
+    except ImportError:
+        # Runtime fallback for Python 3.9 without typing_extensions
+        class TypeGuard:
+            def __class_getitem__(cls, key):
+                return bool
+
+
+class StructSerializable(Protocol):
+    """Any type that can be serialized or deserialized as a WPILib Struct."""
+
+    WPIStruct: ClassVar
+
+
+def is_wpistruct_type(cls: type) -> TypeGuard[type[StructSerializable]]:
+    """Returns True if the given type supports WPILib Struct serialization."""
+    return hasattr(cls, "WPIStruct")