more accurate FPS forESP32

the standard millis() code is very inaccurate in the "high FPS" ranges. This replaces it with the esp32 high resolution timer.

wled00/FX.cpp

@@ -2809,7 +2809,7 @@ uint16_t mode_bouncing_balls(void) {
       // number of balls based on intensity setting to max of 7 (cycles colors)
       // non-chosen color is a random color
       uint16_t numBalls = (SEGMENT.intensity * (maxNumBalls - 1)) / 255 + 1; // minimum 1 ball
-      const float gravity = -9.81; // standard value of gravity
+      constexpr float gravity = -9.81; // standard value of gravity
       const bool hasCol2 = SEGCOLOR(2);
       const unsigned long time = millis();