Add Volcengine support for TTS and ASR services

- Introduced Volcengine as a new provider for both TTS and ASR services.
- Updated configuration files to include Volcengine-specific parameters such as app_id, resource_id, and uid.
- Enhanced the ASR service to support streaming mode with Volcengine's API.
- Modified existing tests to validate the integration of Volcengine services.
- Updated documentation to reflect the addition of Volcengine as a supported provider for TTS and ASR.
- Refactored service factory to accommodate Volcengine alongside existing providers.

engine/tests/test_tts_factory_modes.py

@@ -0,0 +1,45 @@
+from providers.factory.default import DefaultRealtimeServiceFactory
+from providers.tts.mock import MockTTSService
+from providers.tts.openai_compatible import OpenAICompatibleTTSService
+from providers.tts.volcengine import VolcengineTTSService
+from runtime.ports import TTSServiceSpec
+
+
+def test_create_tts_service_volcengine_returns_native_provider():
+    factory = DefaultRealtimeServiceFactory()
+    service = factory.create_tts_service(
+        TTSServiceSpec(
+            provider="volcengine",
+            api_key="test-key",
+            app_id="app-1",
+            resource_id="seed-tts-2.0",
+            voice="zh_female_shuangkuaisisi_moon_bigtts",
+            sample_rate=16000,
+        )
+    )
+    assert isinstance(service, VolcengineTTSService)
+
+
+def test_create_tts_service_openai_compatible_returns_provider():
+    factory = DefaultRealtimeServiceFactory()
+    service = factory.create_tts_service(
+        TTSServiceSpec(
+            provider="openai_compatible",
+            api_key="test-key",
+            voice="anna",
+            sample_rate=16000,
+        )
+    )
+    assert isinstance(service, OpenAICompatibleTTSService)
+
+
+def test_create_tts_service_fallbacks_to_mock_without_key():
+    factory = DefaultRealtimeServiceFactory()
+    service = factory.create_tts_service(
+        TTSServiceSpec(
+            provider="volcengine",
+            voice="anna",
+            sample_rate=16000,
+        )
+    )
+    assert isinstance(service, MockTTSService)