DeprecationWarning in PlatformEventManager

[vdusek]

We should probably not do this:

class PlatformEventManager(EventManager):
    _connected_to_platform_websocket: asyncio.Future = asyncio.Future()

Warning:

apify/_platform_event_manager.py:138
  /home/vdusek/Projects/crawlee-python/.venv/lib/python3.13/site-packages/apify/_platform_event_manager.py:138: DeprecationWarning: There is no current event loop
    _connected_to_platform_websocket: asyncio.Future = asyncio.Future()

The _connected_to_platform_websocket should be initialized to None, and the Future instance can be created lazily.