AR: fastpath optimizations

Some optimizations in FASTPATH mode, to ensure that audio processing takes places as soon as new samples are arriving:
* raise fftTask prio to 4 (above async_tcp) - to ensure that other gimmicks (MQTT, IR, alexa, live preview (ws), json API, or web UI) cannot cause delays by preempting audio.
* changed the "be nice" condition in AR::loop

usermods/audioreactive/audio_reactive.h

@@ -25,9 +25,14 @@
 //#define SR_STATS
 
 #if !defined(FFTTASK_PRIORITY)
+#if defined(WLEDMM_FASTPATH) && !defined(CONFIG_IDF_TARGET_ESP32S2) && !defined(CONFIG_IDF_TARGET_ESP32C3) && defined(ARDUINO_ARCH_ESP32)
+// FASTPATH: use higher priority, to avoid that webserver (ws, json, etc) delays sample processing
+//#define FFTTASK_PRIORITY 3 // competing with async_tcp
+#define FFTTASK_PRIORITY 4   // above async_tcp
+#else
 #define FFTTASK_PRIORITY 1 // standard: looptask prio
 //#define FFTTASK_PRIORITY 2 // above looptask, below async_tcp
-//#define FFTTASK_PRIORITY 4 // above async_tcp
+#endif
 #endif
 
 #if !defined(CONFIG_IDF_TARGET_ESP32S2) && !defined(CONFIG_IDF_TARGET_ESP32C3)
@@ -499,6 +504,11 @@ void FFTcode(void * parameter)
     }
 #endif
 
+#if defined(WLEDMM_FASTPATH) && !defined(CONFIG_IDF_TARGET_ESP32S2) && !defined(CONFIG_IDF_TARGET_ESP32C3) && defined(ARDUINO_ARCH_ESP32)
+    // experimental - be nice to LED update task (trying to avoid flickering) - dual core only
+    if (strip.isServicing()) delay(2);
+#endif
+
     // band pass filter - can reduce noise floor by a factor of 50
     // downside: frequencies below 100Hz will be ignored
    if ((useInputFilter > 0) && (useInputFilter < 99)) {
@@ -1881,7 +1891,7 @@ class AudioReactive : public Usermod {
         return;
       }
       // We cannot wait indefinitely before processing audio data
-      if (strip.isUpdating() && (millis() - lastUMRun < 2)) return;   // be nice, but not too nice
+      if (strip.isServicing() && (millis() - lastUMRun < 2)) return;   // WLEDMM isServicing() is the critical part (be nice, but not too nice)
 
       // suspend local sound processing when "real time mode" is active (E131, UDP, ADALIGHT, ARTNET)
       if (  (realtimeOverride == REALTIME_OVERRIDE_NONE)  // please add other overrides here if needed