Python: Improve agent integration tests

[moonbox3]

Motivation and Context

The current integration tests for agents work fine; however, if any errors are encountered due to server-side hiccups, the instant failure cause the whole test run to fail. This PR creates an agent_test_base that provides some retry logic, as well as a standardized way for agent test classes to use the underlying methods/protocol.

Description

Improve the agent integration tests.

• The OpenAI Responses API is throwing 500s for file search right now. Adding xfail for the time being. Filed an issue on them.
• Handle errors when calling for a response for the OpenAI Responses API -- throw a specific agent except or content exception, if received from Azure OpenAI.
• Removed the OpenAIResponsesAgent invoke and invoke_stream web_search tests. We have coverage for get_responses. The web search is flaky sometimes.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[markwallace-microsoft]

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3418	5 💤	0 ❌	0 🔥	1m 41s ⏱️