Implement DashScope ASR provider and enhance ASR service architecture

- Added DashScope ASR service implementation for real-time streaming.
- Updated ASR provider logic to support DashScope alongside existing providers.
- Enhanced runtime metadata resolution to include DashScope as a valid ASR provider.
- Modified configuration files and documentation to reflect the addition of DashScope.
- Introduced tests to validate DashScope integration and ASR service behavior.
- Refactored ASR service factory to accommodate new provider options and modes.

engine/app/config.py

@@ -85,7 +85,7 @@ class Settings(BaseSettings):
     # ASR Configuration
     asr_provider: str = Field(
         default="openai_compatible",
-        description="ASR provider (openai_compatible, buffered, siliconflow)"
+        description="ASR provider (openai_compatible, buffered, siliconflow, dashscope)"
     )
     asr_api_url: Optional[str] = Field(default=None, description="ASR provider API URL")
     asr_model: Optional[str] = Field(default=None, description="ASR model name")