Python: missing `packaging` dependency in `agent-framework-core`

[moonbox3]

Follow these steps to repro the issue:

# 1. Create a clean virtual environment
uv venv test-env

# 2. Activate it
source test-env/bin/activate

# 3. Install agent-framework-core with minimal dependencies
uv pip install agent-framework-core==1.0.0b251104

# 4. Try to import Azure OpenAI client
python -c "from agent_framework.azure import AzureOpenAIChatClient"

It's expected that this succeeds; however, it currently fails with: `ModuleNotFoundError: No module named 'packaging'

Looks like OpenAI's _shared.py line 20 imports from packaging import version and packaging is not declared in agent-framework-core dependencies.