feat: integrate Opus codec into lib/libopus + voice messages in chatgui

- Add lib/libopus/ (opus v1.6.1 embedded source: CELT 18 .c, SILK 77 .c, SILK float 28 .c, OPUS core 14 .c)
- Add lib/opus_codec.h/.c (wrapper: encoder, decoder, raw PCM int16)
- Add tests/test_opus_codec.c (7 tests: silence, sine, compression, PLC, null, defaults, multi-frame)
- chatgui: AudioRecorder (miniaudio capture, 48kHz mono)
- chatgui: VoiceEncoder (PCM→Opus file with custom container)
- chatgui: VoicePlayer (Opus→PCM playback via SoundManager)
- chatgui: PTT button in InputBar, voice message send/receive in MessageList
- chatgui: AudioDeviceSettingsPage (device selection, persisted in ui_state)
- chatgui: MessageDelegate voice message rendering (play button + duration)
- Update autotools: configure.ac, Makefile.am, src/Makefile.am, tests/Makefile.am
- Update CMake: chatgui CMakeLists.txt, libutun CMakeLists.txt (link libopus_internal.a)

lib/libopus/silk/init_decoder.c

@@ -0,0 +1,83 @@
+/***********************************************************************
+Copyright (c) 2006-2011, Skype Limited. All rights reserved.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+- Redistributions of source code must retain the above copyright notice,
+this list of conditions and the following disclaimer.
+- Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in the
+documentation and/or other materials provided with the distribution.
+- Neither the name of Internet Society, IETF or IETF Trust, nor the
+names of specific contributors, may be used to endorse or promote
+products derived from this software without specific prior written
+permission.
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+***********************************************************************/
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "main.h"
+
+#ifdef ENABLE_OSCE
+#include "osce.h"
+#endif
+
+#include "structs.h"
+
+/************************/
+/* Reset Decoder State  */
+/************************/
+opus_int silk_reset_decoder(
+    silk_decoder_state          *psDec                          /* I/O  Decoder state pointer                       */
+)
+{
+    /* Clear the entire encoder state, except anything copied */
+    silk_memset( &psDec->SILK_DECODER_STATE_RESET_START, 0, sizeof( silk_decoder_state ) - ((char*) &psDec->SILK_DECODER_STATE_RESET_START - (char*)psDec) );
+
+    /* Used to deactivate LSF interpolation */
+    psDec->first_frame_after_reset = 1;
+    psDec->prev_gain_Q16 = 65536;
+    psDec->arch = opus_select_arch();
+
+    /* Reset CNG state */
+    silk_CNG_Reset( psDec );
+
+    /* Reset PLC state */
+    silk_PLC_Reset( psDec );
+
+#ifdef ENABLE_OSCE
+    /* Reset OSCE state and method */
+    osce_reset(&psDec->osce, OSCE_DEFAULT_METHOD);
+#endif
+
+    return 0;
+}
+
+
+/************************/
+/* Init Decoder State   */
+/************************/
+opus_int silk_init_decoder(
+    silk_decoder_state          *psDec                          /* I/O  Decoder state pointer                       */
+)
+{
+    /* Clear the entire encoder state, except anything copied */
+    silk_memset( psDec, 0, sizeof( silk_decoder_state ) );
+
+    silk_reset_decoder( psDec );
+
+    return(0);
+}