Add Inworld Realtime Service (#4140)

* Add Inworld Realtime LLM service

Adds a WebSocket-based realtime service for Inworld's cascade
STT/LLM/TTS API with semantic VAD, function calling, and streaming
transcription support.

New files:
- src/pipecat/services/inworld/realtime/ (service, events)
- src/pipecat/adapters/services/inworld_realtime_adapter.py
- examples/foundational/19zb-inworld-realtime.py

Also includes:
- websockets dependency for inworld extra in pyproject.toml
- Adapter and settings tests matching OpenAI/Grok realtime patterns
- Fix for double-response when server-side VAD is enabled

* Prefer init-provided system instruction in Inworld Realtime

Adopt _resolve_system_instruction() from BaseLLMAdapter, matching the
pattern applied to OpenAI Realtime, Grok Realtime, Gemini Live, and
Nova Sonic in the pk/realtime-services-init-v-context-system-instructions-cleanup
branch.

* Update changelog entry with PR number

* Fix changelog format to use bullet point

* Polish PR: default model, example cleanup, changelog update

- Change default model from gpt-4.1-nano to gpt-4.1-mini
- Add function calling demo to example
- Remove demo-testing artifact from system instruction
- Mention Router support in changelog

* Address PR review feedback for Inworld Realtime

- Move example to examples/realtime/realtime-inworld.py
- Change initial context role from "user" to "developer"
- Remove explicit sample rates from example; sync them in
  _ensure_audio_config so Inworld gets the transport's actual rates
- Add audio race condition guard in _handle_evt_audio_delta (matches
  OpenAI realtime pattern)
- Convert remaining "system"/"developer" messages to "user" in adapter
- Add clarifying comment for local-VAD vs server-VAD metrics paths

* Simplify example, add provider tracking, remove local VAD path

- Remove function calling from example, switch model to xai/grok-4-1-fast-non-reasoning
- Add pipecat-realtime session key prefix and provider_data metadata
  for Inworld traffic attribution
- Remove local VAD code path (Inworld only supports server-side VAD)
- Use typed InputAudioBufferAppendEvent for audio sends

* Default TTS model to inworld-tts-1.5-max

* Remove dead shimmed tools code, set STT/VAD defaults

- Remove non-functional AdapterType.SHIM custom tools code from adapter
- Default STT model to assemblyai/u3-rt-pro
- Default VAD eagerness to low

tests/test_function_calling_adapters.py

@@ -13,6 +13,7 @@ from pipecat.adapters.schemas.tools_schema import AdapterType, ToolsSchema
 from pipecat.adapters.services.anthropic_adapter import AnthropicLLMAdapter
 from pipecat.adapters.services.bedrock_adapter import AWSBedrockLLMAdapter
 from pipecat.adapters.services.gemini_adapter import GeminiLLMAdapter
+from pipecat.adapters.services.inworld_realtime_adapter import InworldRealtimeLLMAdapter
 from pipecat.adapters.services.open_ai_adapter import OpenAILLMAdapter
 from pipecat.adapters.services.open_ai_realtime_adapter import OpenAIRealtimeLLMAdapter
 
@@ -143,6 +144,32 @@ class TestFunctionAdapters(unittest.TestCase):
         ]
         assert OpenAIRealtimeLLMAdapter().to_provider_tools_format(self.tools_def) == expected
 
+    def test_inworld_realtime_adapter(self):
+        """Test Inworld Realtime adapter format transformation."""
+        expected = [
+            {
+                "type": "function",
+                "name": "get_weather",
+                "description": "Get the weather in a given location",
+                "parameters": {
+                    "type": "object",
+                    "properties": {
+                        "location": {
+                            "type": "string",
+                            "description": "The city, e.g. San Francisco",
+                        },
+                        "format": {
+                            "type": "string",
+                            "enum": ["celsius", "fahrenheit"],
+                            "description": "The temperature unit to use.",
+                        },
+                    },
+                    "required": ["location", "format"],
+                },
+            }
+        ]
+        assert InworldRealtimeLLMAdapter().to_provider_tools_format(self.tools_def) == expected
+
     def test_gemini_adapter_with_custom_tools(self):
         """Test Gemini adapter format transformation."""
         search_tool = {"google_search": {}}