fix include/namespace related compilation errors (#7019)

a user on discord reported compilation errors when trying to compile
on Linux with GCC 13 and Clang 16.

src/audio_core/time_stretch.cpp

@@ -10,8 +10,10 @@
 #include <type_traits>
 #include <vector>
 #include <SoundTouch.h>
+
 #include "audio_core/audio_types.h"
 #include "audio_core/time_stretch.h"
+#include "common/assert.h"
 #include "common/logging/log.h"
 
 namespace AudioCore {