usb: unify ControlHandler+DeviceStateHandler, route all control requests to all handlers.

- Allows classes to handle vendor requests.
- Allows classes to use a single handler for multiple interfaces.
- Allows classes to access the other events (previously only `reset` was available).

embassy-usb/gen_config.py

@@ -28,6 +28,7 @@ def feature(name, default, min, max, pow2=None):
 
 
 feature("max_interface_count", default=4, min=1, max=8)
+feature("max_handler_count", default=4, min=1, max=8)
 
 # ========= Update Cargo.toml