No compromises for the manage_heater()

No compromises for the manage_heater(). manage_heater() will return immediately when there is nothing to do, but needs a constant detaT to work proper.
Calling idle() only every 200ms results in a display update every ~2 seconds - that should be enough.
For the other functionalities in idle() and manage_inactivity() 200ms is a lot but hopefully works.

Marlin/Configuration_adv.h

 // @section extras
 
 // Arc interpretation settings:
-#define ARC_SUPPORT  // Disabling this saves ~2660bytes
+#define ARC_SUPPORT  // Disabling this saves ~2738 bytes
 #define MM_PER_ARC_SEGMENT 1
 #define N_ARC_CORRECTION 25
 
-// Support for G5 with XYZE destination and IJPQ offsets
+// Support for G5 with XYZE destination and IJPQ offsets. Needs ~2666 bytes
 //#define BEZIER_CURVE_SUPPORT
 
 const unsigned int dropsegments = 5; //everything with less than this number of steps will be ignored as move and joined with the next movement

Marlin/Marlin_main.cpp

 
     float feed_rate = feedrate * feedrate_multiplier / 60 / 100.0;
 
-    millis_t previous_ms = millis();
+    millis_t next_ping_ms = millis() + 200UL;
 
     for (i = 1; i < segments; i++) { // Iterate (segments-1) times
 
+      thermalManager.manage_heater();
       millis_t now = millis();
-      if (now - previous_ms > 200UL) {
-        previous_ms = now;
+      if (ELAPSED(now, next_ping_ms)) {
+        next_ping_ms = now + 200UL;
         idle();
       }
 

Marlin/planner_bezier.cpp

   bez_target[Y_AXIS] = position[Y_AXIS];
   float step = MAX_STEP;
 
-  uint8_t idle_counter = 0;
   millis_t next_ping_ms = millis() + 200UL;
 
   while (t < 1.0) {
 
+    thermalManager.manage_heater();
     millis_t now = millis();
     if (ELAPSED(now, next_ping_ms)) {
       next_ping_ms = now + 200UL;
-      (idle_counter++ & 0x03) ? thermalManager.manage_heater() : idle();
+      idle();
     }
 
     // First try to reduce the step in order to make it sufficiently