audio.cpp 0.4 adds Higgs Audio v3 TTS, Fish Audio S2 Pro, GGUF loading

audio.cpp 0.4 brings Higgs Audio v3 TTS 4B (10x real-time), Fish Audio S2 Pro, Voxtral Realtime ASR, OuteTTS, and VieNeu-TTS-v3 to C++/GGML, plus first-class GGUF loading and Q8 speed/VRAM gains.