refactor: streamline auth handling and CLI structure

- Added `fallback_model = "deepseek"` to `PollinationsAI` class in `PollinationsAI.py`
- Modified `PollinationsAI._agenerate` to safely call `get_model` only if `model` is not None
- Removed unused login loop in `OpenaiChat.synthesize` method in `OpenaiChat.py`
- Replaced full CLI parser and main function implementation in `__main__.py` with import from `.main`
- Added `get_auth_result` method to `AsyncAuthedProvider` in `base_provider.py` for reusable auth retrieval
- Replaced repeated auth loading logic in `create_completion` and `create_streaming_completion` with call to `get_auth_result` in `base_provider.py

g4f/Provider/needs_auth/OpenaiChat.py

@@ -603,8 +603,6 @@ class OpenaiChat(AsyncAuthedProvider, ProviderModelMixin):
 
     @classmethod
     async def synthesize(cls, params: dict) -> AsyncIterator[bytes]:
-        async for _ in cls.login():
-            pass
         async with StreamSession(
             impersonate="chrome",
             timeout=0