.Net Bug: OpenAIResponseAgent does not provide messages to AIContext for streaming

**Describe the bug**
A clear and concise description of what the bug is.

**To Reproduce**
Run integration/conformance test:

`OpenAIResponseAgentWithAIContextProviderTests.StatePartReceivesMessagesFromAgentWhenStreamingAsync`

**Platform**
 - Language: C#
 - Source: `main`
 - OS: Windows
