feat: ASR 从双向流式切换为流式输入模式（bigmodel_nostream）

- endpoint 从 bigmodel_async 改为 bigmodel_nostream
- 二进制协议去掉 sequence 字段，初始请求和音频帧均不带序号
- 最后一帧使用 FlagLastNoSeq 标志
- RequestMeta 新增 result_type=single、end_window_size=400
- ShowUtterances 关闭（nostream 模式不需要）
- readLoop 简化：nostream 模式下直接返回 final 结果

internal/asr/protocol.go

@@ -109,9 +109,12 @@ type RequestMeta struct {
 	EnablePUNC     bool   `json:"enable_punc"`
 	EnableDDC      bool   `json:"enable_ddc"`
 	ShowUtterances bool   `json:"show_utterances"`
+	ResultType     string `json:"result_type,omitempty"`
+	EndWindowSize  int    `json:"end_window_size,omitempty"`
 }
 // EncodeFullClientRequest builds the binary message for the initial handshake.
-func EncodeFullClientRequest(req *FullClientRequest, seq int32) ([]byte, error) {
+// nostream mode: header(4) + payload_size(4) + gzip(json)
+	func EncodeFullClientRequest(req *FullClientRequest) ([]byte, error) {
 	payloadJSON, err := json.Marshal(req)
 	if err != nil {
 		return nil, fmt.Errorf("marshal request: %w", err)
@@ -121,20 +124,18 @@ func EncodeFullClientRequest(req *FullClientRequest, seq int32) ([]byte, error)
 		return nil, fmt.Errorf("gzip compress: %w", err)
 	}
 	var buf bytes.Buffer
-	buf.Write(encodeHeader(MsgFullClientRequest, FlagPosSeq, SerJSON, CompGzip))
-	_ = binary.Write(&buf, binary.BigEndian, seq)
+	buf.Write(encodeHeader(MsgFullClientRequest, FlagNoSeq, SerJSON, CompGzip))
 	_ = binary.Write(&buf, binary.BigEndian, int32(len(compressed)))
 	buf.Write(compressed)
 	return buf.Bytes(), nil
 }
 // EncodeAudioFrame builds a binary audio-only request.
-// If last is true, seq is sent as negative to signal end of stream.
-func EncodeAudioFrame(seq int32, pcm []byte, last bool) ([]byte, error) {
-	flags := FlagPosSeq
-	wireSeq := seq
+// nostream mode: header(4) + payload_size(4) + gzip(pcm)
+// last=true sets FlagLastNoSeq to signal end of stream.
+func EncodeAudioFrame(pcm []byte, last bool) ([]byte, error) {
+	flags := FlagNoSeq
 	if last {
-		flags = FlagNegSeq
-		wireSeq = -seq
+		flags = FlagLastNoSeq
 	}
 	compressed, err := gzipCompress(pcm)
 	if err != nil {
@@ -142,7 +143,6 @@ func EncodeAudioFrame(seq int32, pcm []byte, last bool) ([]byte, error) {
 	}
 	var buf bytes.Buffer
 	buf.Write(encodeHeader(MsgAudioOnlyRequest, flags, SerNone, CompGzip))
-	_ = binary.Write(&buf, binary.BigEndian, wireSeq)
 	_ = binary.Write(&buf, binary.BigEndian, int32(len(compressed)))
 	buf.Write(compressed)
 	return buf.Bytes(), nil