Consolidate States/DEFAULT_THRESHOLDS into temp_controller_base.py

tc_constants.py only held States and DEFAULT_THRESHOLDS, both used
exclusively by temp_controller_base.py and its subclasses; fold them
into temp_controller_base.py directly and drop the now-empty module.
Also drop heat_diffusion.py, unused since pot.py switched to the
delay-line model, and the matching dead import in pot.py.

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

components/plant/heat_diffusion.py

@@ -1,23 +0,0 @@
-import numpy as np
-
-
-class HeatDiffusion:
-	def __init__(self, dt, delay, ic=0):
-		self.alpha = dt/delay
-		self.beta = 1 - self.alpha
-		self.state = ic
-
-	def initial(self, ic):
-		self.state = ic
-
-	def process(self, x):
-		self.state = self.beta * self.state + self.alpha*x
-		return self.state
-
-
-if __name__ == '__main__':
-	d = HeatDiffusion(0.1, 1)
-
-	for i in range(1, 200):
-		y = d.process(1)
-		print("In = {}, out = {}".format(i, y))

components/plant/pot.py

@@ -1,5 +1,4 @@
 from components.aplant import APlant
-from components.plant.heat_diffusion import HeatDiffusion
 from components.plant import delay
 
 class Pot(APlant):