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/pid/temp_controller_base.py

@@ -1,9 +1,24 @@
 from components import APid
 from components.pid.pid import Pid
-from components.pid.tc_constants import States, DEFAULT_THRESHOLDS
+import enum
 
+DEFAULT_THRESHOLDS = {
+	"HoldIdle": 0.1,
+	"HoldHeat": 1.0,
+	"IdleHeat": 1.0,
+	"IdleHold": 0.1,
+	"HeatHold": 1.0,
+	"HeatIdle": 1.0
+}
+
+class States(enum.Enum):
+	INIT = -1,
+	IDLE = 0,
+	HEAT = 1,
+	HOLD = 2
 
 class TempControllerBase(APid):
+
 	def __init__(self, dt, params):
 		APid.__init__(self)
 		self.pid_hold = Pid(dt)