more advanced build script, refactor eqprocessor.cpps functions: process and recomputeBiquad, which were not nice to read. now nicer to read. no need to compile, compile at more major change

src/engine/EqProcessor.h

@@ -1,5 +1,4 @@
 #pragma once
-#include <array>
 #include "AudioBuffer.h"
 
 namespace engine {
@@ -28,10 +27,23 @@ private:
     int   m_sampleRate { 44100 };
     float m_gainDb[BANDS] {};
 
-    float m_coeff[BANDS][5] {};
+    struct BiquadCoefficients {
+        float b0 {};
+        float b1 {};
+        float b2 {};
+        float a1 {};
+        float a2 {};
+    };
+
+    BiquadCoefficients m_coeff[BANDS];
+
+    struct BiquadState {
+        float z1;
+        float z2;
+    };
 
     static constexpr int MAX_CH = 8;
-    float m_state[BANDS][MAX_CH][2] {};
+    BiquadState m_state[BANDS][MAX_CH] {};
 };
 
 } // namespace engine