Improve slim docker image example, clean up OpenaiChat provider (#2397)

* Improve slim docker image example, clean up OpenaiChat provider

* Enhance event loop management for asynchronous generators

* Fix attribute " shutdown_default_executor" not found in old python versions

* asyncio file added with all async helpers

g4f/providers/asyncio.py

@@ -0,0 +1,65 @@
+from __future__ import annotations
+
+import asyncio
+from asyncio import AbstractEventLoop, runners
+from typing import Union, Callable, AsyncGenerator, Generator
+
+from ..errors import NestAsyncioError
+
+try:
+    import nest_asyncio
+    has_nest_asyncio = True
+except ImportError:
+    has_nest_asyncio = False
+try:
+    import uvloop
+    has_uvloop = True
+except ImportError:
+    has_uvloop = False
+
+def get_running_loop(check_nested: bool) -> Union[AbstractEventLoop, None]:
+    try:
+        loop = asyncio.get_running_loop()
+        # Do not patch uvloop loop because its incompatible.
+        if has_uvloop:
+            if isinstance(loop, uvloop.Loop):
+               return loop
+        if not hasattr(loop.__class__, "_nest_patched"):
+            if has_nest_asyncio:
+                nest_asyncio.apply(loop)
+            elif check_nested:
+                raise NestAsyncioError('Install "nest_asyncio" package | pip install -U nest_asyncio')
+        return loop
+    except RuntimeError:
+        pass
+
+# Fix for RuntimeError: async generator ignored GeneratorExit
+async def await_callback(callback: Callable):
+    return await callback()
+
+async def async_generator_to_list(generator: AsyncGenerator) -> list:
+    return [item async for item in generator]
+
+def to_sync_generator(generator: AsyncGenerator) -> Generator:
+    loop = get_running_loop(check_nested=False)
+    new_loop = False
+    if loop is None:
+        loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(loop)
+        new_loop = True
+    gen = generator.__aiter__()
+    try:
+        while True:
+            yield loop.run_until_complete(await_callback(gen.__anext__))
+    except StopAsyncIteration:
+        pass
+    finally:
+        if new_loop:
+            try:
+                runners._cancel_all_tasks(loop)
+                loop.run_until_complete(loop.shutdown_asyncgens())
+                if hasattr(loop, "shutdown_default_executor"):
+                    loop.run_until_complete(loop.shutdown_default_executor())
+            finally:
+                asyncio.set_event_loop(None)
+                loop.close()