Description: Fixes issue #2688 by upgrading httpx-aiohttp from 0.1.8 to 0.1.9 to resolve production timeout issues when using the aiohttp backend.

Changes:

• Updated 'pyproject.toml' to require 'httpx_aiohttp>=0.1.9'
• Updated 'requirements.lock' and 'requirements-dev.lock' to use 'httpx-aiohttp==0.1.9'
• Added an example demonstrating aiohttp backend usage and timeout handling

Testing:

• Verified httpx-aiohttp 0.1.9 is properly installed
• Tested basic connectivity with aiohttp backend
• Tested concurrent requests (common timeout scenario)
• Tested timeout handling and error recovery
• Tested production-ready retry logic

Impact:
This upgrade resolves timeout issues that users experienced in production when using:

pip install openai[aiohttp]
client = AsyncOpenAI(http_client=DefaultAioHttpClient())

Fixes #2688