refactor: move iir_filter to separate compilation unit

pasada-lib/include/iir_filter.h

@@ -0,0 +1,46 @@
+//
+// Created by david on 02.03.2026.
+//
+
+#ifndef PASADASUPERPROJECT_IIR_FILTER_H
+#define PASADASUPERPROJECT_IIR_FILTER_H
+
+#include <utility>
+#include <vector>
+#include <stdexcept>
+
+/** Shift register implemented as a circular buffer. */
+class Buf {
+protected:
+    std::vector<double> data;
+    size_t size;
+    size_t n;
+public:
+    Buf(size_t N);
+    void push(double val);
+};
+
+/** Running filter base. */
+class Filt : Buf {
+protected:
+    std::vector<double> taps;
+    size_t shift;
+    size_t offset;
+public:
+    Filt(size_t N, size_t shift, size_t offset, std::vector<double> taps);
+    double filter(double val);
+    double peek();
+    void push(double val);
+};
+
+/** Running IIR filter. */
+class IirFilter {
+protected:
+    Filt y;
+    Filt x;
+public:
+    IirFilter(std::vector<double> b, std::vector<double> a);
+    double filter(double val);
+};
+
+#endif //PASADASUPERPROJECT_IIR_FILTER_H