Allow controlling ServiceSwitcher with either immediate frames (SystemFrames) or in-order frames (ControlFrames).

Immediate is the "default", i.e. has the more obvious name (e.g. `ManuallySwitchServiceFrame` v `ManuallySwitchServiceControlFrame`), since that's *probably* what users will want to reach for. Also, the immediate frames are more likely to behave like what we had before the last few commits, where the service switch would always "jump the queue" by having an immediate effect once it hit the `ServiceSwitcher` in the pipeline, jumping ahead of frames in front of it destined for the service.

src/pipecat/frames/frames.py

@@ -1603,17 +1603,46 @@ class MixerEnableFrame(MixerControlFrame):
 
 
 @dataclass
-class ServiceSwitcherFrame(ControlFrame):
-    """A base class for frames that control ServiceSwitcher behavior."""
+class ManuallySwitchServiceBaseFrame:
+    """Base class for frames that request a manual service switch from a ServiceSwitcher.
+
+    Must be inherited alongside either ServiceSwitcherFrame or ServiceSwitcherControlFrame.
+    """
+
+    service: "FrameProcessor"
+
+
+@dataclass
+class ServiceSwitcherFrame(SystemFrame):
+    """A base class for frames that affect ServiceSwitcher behavior immediately."""
 
     pass
 
 
 @dataclass
-class ManuallySwitchServiceFrame(ServiceSwitcherFrame):
-    """A frame to request a manual switch in the active service in a ServiceSwitcher.
+class ManuallySwitchServiceFrame(ServiceSwitcherFrame, ManuallySwitchServiceBaseFrame):
+    """A frame to request an immediate manual switch in the active service in a ServiceSwitcher.
 
     Handled by ServiceSwitcherStrategyManual to switch the active service.
     """
 
-    service: "FrameProcessor"
+    pass
+
+
+@dataclass
+class ServiceSwitcherControlFrame(ControlFrame):
+    """A base class for frames that affect ServiceSwitcher behavior, in order."""
+
+    pass
+
+
+@dataclass
+class ManuallySwitchServiceControlFrame(
+    ServiceSwitcherControlFrame, ManuallySwitchServiceBaseFrame
+):
+    """A frame to request a manual switch in the active service in a ServiceSwitcher, in order.
+
+    Handled by ServiceSwitcherStrategyManual to switch the active service.
+    """
+
+    pass