Force the heater off and show a "Cool down" indicator during a passive cooldown

A ramp step whose target is below the current actual temperature can
only be reached by ambient cooling - the heater can't actively cool.
SudTask now detects this once per ramp phase and calls the controller's
new set_cooling() override (forces y=0, bypassing the FSM) instead of
waiting for its hysteresis-based IDLE transition. The GUI shows a
blinking blue "Cool down" label in the status bar while this is active.
Progression already only advances once theta_ist matches theta_soll
regardless of direction, so no change was needed there.

components/pid/temp_controller_base.py

@@ -37,6 +37,12 @@ class TempControllerBase(APid):
 		self.pid_hold.set_params(params['Hold'])
 		self.pid_rate.set_params(params['Heat'])
 		self.is_startup = True
+		# Explicit override for a ramp step whose target is below the
+		# current temperature: the heater can't actively cool, so rather
+		# than wait for the FSM's own (slower, hysteresis-based) IDLE
+		# transition, force y to 0 as soon as the caller (SudTask) knows
+		# the step needs to passively cool down.
+		self.cooling = False
 
 	def on_state_entered(self, state):
 		pass
@@ -70,6 +76,9 @@ class TempControllerBase(APid):
 	def set_heatrate_soll(self, value):
 		self.heatrate_soll_set = value
 
+	def set_cooling(self, value):
+		self.cooling = value
+
 	def get_heatrate_soll(self):
 		return self.heatrate_soll
 
@@ -109,7 +118,7 @@ class TempControllerBase(APid):
 		self.pid_hold.process(theta_err, -self.theta_ist, hold_scale)
 		self.pid_rate.process(heatrate_err, -self.heatrate_ist)
 
-		if self.state == States.IDLE:
+		if self.state == States.IDLE or self.cooling:
 			self.y = 0
 		else:
 			self.y = self.pid_rate.get_y()