motion_queuing: Track all trapqs and globally flush all trapqs

Add an allocate_trapq() helper function to facilitate the creation of
a low-level C trapq object.  Track all trapq objects and clear history
on them globally when the main motion queues are flushed.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/kinematics/extruder.py

@@ -163,10 +163,9 @@ class PrinterExtruder:
         self.instant_corner_v = config.getfloat(
             'instantaneous_corner_velocity', 1., minval=0.)
         # Setup extruder trapq (trapezoidal motion queue)
-        ffi_main, ffi_lib = chelper.get_ffi()
-        self.trapq = ffi_main.gc(ffi_lib.trapq_alloc(), ffi_lib.trapq_free)
-        self.trapq_append = ffi_lib.trapq_append
-        self.trapq_finalize_moves = ffi_lib.trapq_finalize_moves
+        self.motion_queuing = self.printer.load_object(config, 'motion_queuing')
+        self.trapq = self.motion_queuing.allocate_trapq()
+        self.trapq_append = self.motion_queuing.lookup_trapq_append()
         # Setup extruder stepper
         self.extruder_stepper = None
         if (config.get('step_pin', None) is not None