refactor: moved registries into a separate module and code cleanup

fix: refactored dial provider to follow the same pattern

providers/__init__.py

@@ -3,8 +3,8 @@
 from .azure_openai import AzureOpenAIProvider
 from .base import ModelProvider
 from .gemini import GeminiModelProvider
+from .openai import OpenAIModelProvider
 from .openai_compatible import OpenAICompatibleProvider
-from .openai_provider import OpenAIModelProvider
 from .openrouter import OpenRouterProvider
 from .registry import ModelProviderRegistry
 from .shared import ModelCapabilities, ModelResponse