Deduplicate logic for getting request model in `openai-agents`

[alexander-alderman-webb]

Remove duplication between

sentry-python/sentry_sdk/integrations/openai_agents/spans/ai_client.py

Lines 26 to 29 in 53188b3

	if agent.model:
	model_name = agent.model.model if hasattr(agent.model, "model") else agent.model
	elif hasattr(agent, "_sentry_request_model"):
	model_name = agent._sentry_request_model

and

sentry-python/sentry_sdk/integrations/openai_agents/utils.py

Lines 59 to 62 in 53188b3

	if agent.model:
	model_name = agent.model.model if hasattr(agent.model, "model") else agent.model
	elif hasattr(agent, "_sentry_request_model"):
	model_name = agent._sentry_request_model

[linear-code]

PY-2495