Add sensor variance config and smooth heat-rate estimate

[Sensor] - replace TempSensorSim's hardcoded k_noise with configurable
temp_offset/variance, accept **kwargs on Max31865 too so both sensors
share a constructor signature usable from TempSensorFactory.create()
[Temp Controller] - low-pass filter the backward-difference heat-rate
estimate (alpha=0.1) in both temp_controller.py and
temp_controller_smith.py instead of using the raw, noisy derivative
[Pot] - drop kn from demo_pot.py's params, matching the unused-field
removal already made to pot.py itself

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/pid/temp_controller.py

@@ -7,11 +7,14 @@ class TempController(TempControllerBase):
 		self.dt = dt
 		self.last_theta_ist = 20
 		self.heatrate_ist = 0
+
 	def process(self):
 		# Process Kalman
 		self.theta_ist = self.theta_ist_set
 		heatrate = (self.theta_ist - self.last_theta_ist)/self.dt*60
-		self.heatrate_ist = heatrate
+
+		alpha = 0.1
+		self.heatrate_ist = (1-alpha) * self.heatrate_ist + alpha*heatrate
 		self.last_theta_ist = self.theta_ist
 
 		# Compensate for max heat rate to reduce overshoot