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/sensor/tempSensor_max31865.py

@@ -8,7 +8,7 @@ class TempSensor_max31865(ATemperatureSensor):
 	def name(self):
 		return "Max31865"
 
-	def __init__(self, temp_offset=0):
+	def __init__(self, temp_offset=0, **kwargs):
 		ATemperatureSensor.__init__(self)
 		# Open SPI bus
 		self.spi = spidev.SpiDev()