Use T as value type hint in AttributeIO

Author: James Souter

src/fastcs/attribute_io.py

@@ -18,10 +18,7 @@ async def update(
         raise NotImplementedError()
 
     async def send(
-        self,
-        attr: AttrRW[T, AttributeIORefT],
-        ref: AttributeIORefT,
-        value,  # TODO, type this
+        self, attr: AttrRW[T, AttributeIORefT], ref: AttributeIORefT, value: T
     ) -> None:
         raise NotImplementedError()