Add missing header includes for gcc 15.2.0 compatibility

- Add <cstdint> to audio/dsp/Converter.h for uint types
- Add <cstdint> to audio/linux/DeviceManagerPulseAudio.h
- Add <unistd.h> to zlib/gzguts.h for non-Windows platforms

gcc 15.2 has stricter requirements for explicit standard header
includes and no longer transitively includes <cstdint> for integer
types like uint32_t/uint64_t or <unistd.h> for POSIX functions.

Author: andrewfb

include/cinder/audio/dsp/Converter.h

@@ -26,6 +26,7 @@
 #include "cinder/Export.h"
 #include "cinder/audio/Buffer.h"
 
+#include <cstdint>
 #include <memory>
 #include <algorithm>
 

include/cinder/audio/linux/DeviceManagerPulseAudio.h

@@ -24,6 +24,7 @@
 #pragma once
 
 #include "cinder/audio/Device.h"
+#include <cstdint>
 
 namespace cinder { namespace audio { namespace linux {
 

src/zlib/gzguts.h

@@ -30,6 +30,10 @@
 #endif
 #include <fcntl.h>
 
+#ifndef _WIN32
+#  include <unistd.h>
+#endif
+
 #ifdef _WIN32
 #  include <stddef.h>
 #endif