Added tetra rx ext app (#3257)

firmware/application/external/tetra_rx/tetra_viterbi.hpp

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <stdint.h>
+#include <string.h>
+
+namespace ui::external_app::tetra_rx {
+
+class Viterbi {
+   public:
+    int decode_cch(
+        const uint8_t* mother,
+        uint32_t n_info,
+        uint8_t* bits,
+        uint8_t* trace_buffer);
+};
+
+}  // namespace ui::external_app::tetra_rx