feat: Realtime API support reboot (#5392)

* feat(realtime): Initial Realtime API implementation

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

* chore: go mod tidy

Signed-off-by: Richard Palethorpe <io@richiejp.com>

* feat: Implement transcription only mode for realtime API

Reduce the scope of the real time API for the initial realease and make
transcription only mode functional.

Signed-off-by: Richard Palethorpe <io@richiejp.com>

* chore(build): Build backends on a separate layer to speed up core only changes

Signed-off-by: Richard Palethorpe <io@richiejp.com>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Signed-off-by: Richard Palethorpe <io@richiejp.com>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>

pkg/audio/audio.go

@@ -0,0 +1,55 @@
+package audio
+
+// Copied from VoxInput
+
+import (
+  "encoding/binary"
+  "io"
+)
+
+// WAVHeader represents the WAV file header (44 bytes for PCM)
+type WAVHeader struct {
+  // RIFF Chunk (12 bytes)
+  ChunkID   [4]byte
+  ChunkSize uint32
+  Format    [4]byte
+
+  // fmt Subchunk (16 bytes)
+  Subchunk1ID   [4]byte
+  Subchunk1Size uint32
+  AudioFormat   uint16
+  NumChannels   uint16
+  SampleRate    uint32
+  ByteRate      uint32
+  BlockAlign    uint16
+  BitsPerSample uint16
+
+  // data Subchunk (8 bytes)
+  Subchunk2ID   [4]byte
+  Subchunk2Size uint32
+}
+
+func NewWAVHeader(pcmLen uint32) WAVHeader {
+  header := WAVHeader{
+    ChunkID:       [4]byte{'R', 'I', 'F', 'F'},
+    Format:        [4]byte{'W', 'A', 'V', 'E'},
+    Subchunk1ID:   [4]byte{'f', 'm', 't', ' '},
+    Subchunk1Size: 16, // PCM = 16 bytes
+    AudioFormat:   1,  // PCM
+    NumChannels:   1,  // Mono
+    SampleRate:    16000,
+    ByteRate:      16000 * 2, // SampleRate * BlockAlign (mono, 2 bytes per sample)
+    BlockAlign:    2,         // 16-bit = 2 bytes per sample
+    BitsPerSample: 16,
+    Subchunk2ID:   [4]byte{'d', 'a', 't', 'a'},
+    Subchunk2Size: pcmLen,
+  }
+
+  header.ChunkSize = 36 + header.Subchunk2Size
+
+  return header
+}
+
+func (h *WAVHeader) Write(writer io.Writer) error {
+  return binary.Write(writer, binary.LittleEndian, h)
+}