Add stubs for AudioFrame operations

Author: microbit-matt-hillsdon

lang/en/typeshed/stdlib/microbit/audio.pyi

@@ -210,3 +210,9 @@ class AudioFrame:
     def __len__(self) -> int: ...
     def __setitem__(self, key: int, value: int) -> None: ...
     def __getitem__(self, key: int) -> int: ...
+    def __add__(self, v: AudioFrame) -> AudioFrame: ...
+    def __iadd__(self, v: AudioFrame) -> AudioFrame: ...
+    def __sub__(self, v: AudioFrame) -> AudioFrame: ...
+    def __isub__(self, v: AudioFrame) -> AudioFrame: ...
+    def __mul__(self, v: float) -> AudioFrame: ...
+    def __imul__(self, v: float) -> AudioFrame: ...