Make grain_mass/water_mass per-step and re-derive plant params on change

grain_mass and water_mass now live on each step (defaulted from
default.step) instead of being fixed for the whole brew, since both
change over a mash (malt going in, water boiling off).
Sud.derive_plant_params() takes them as arguments so it can be
recomputed per step; the demo re-applies the resulting M/C to both the
real plant and the controller's Smith-predictor model on every step
change via the new Pot.set_thermal_params()/
TempController.set_model_params().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CgR9tPaSzFkAwRAUyeaaCD

components/pid/temp_controller_smith.py

@@ -24,6 +24,10 @@ class TempController(TempControllerBase):
 		self.model.set_power(power)
 		self.model_delay.set_power(power)
 
+	def set_model_params(self, M, C):
+		self.model.set_thermal_params(M, C)
+		self.model_delay.set_thermal_params(M, C)
+
 	def on_state_entered(self, state):
 		if state == States.HEAT:
 			self.model.initial(self.theta_ist)