introduce and push UserSpeakingFrame upstream/downstream

src/pipecat/frames/frames.py

@@ -898,6 +898,16 @@ class UserStoppedSpeakingFrame(SystemFrame):
     emulated: bool = False
 
 
+@dataclass
+class UserSpeakingFrame(SystemFrame):
+    """Frame indicating the user is speaking.
+
+    Emitted by VAD to indicate the user is speaking.
+    """
+
+    pass
+
+
 @dataclass
 class EmulateUserStartedSpeakingFrame(SystemFrame):
     """Frame to emulate user started speaking behavior.