.Net: Include streaming tool call information in model diagnostics

[TaoChenOSU]

Motivation and Context

Tool call information is currently not included in the model diagnostics when using the streaming APIs.

Description

1. Record OpenAI tool call information in model diagnostics for the streaming API.
2. If there is no tool call information, do not record an empty entry.

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 😄

[stephentoub]

Do the other connectors that currently support function calling (Gemini, Mistral) have a similar problem?

[TaoChenOSU]

Do the other connectors that currently support function calling (Gemini, Mistral) have a similar problem?

I intentionally did not record the tool calls information in the Gemini connector, since it's going to adapt to the FunctionCallContent and migrate to the new function call abstractions.

[TaoChenOSU]

Do the other connectors that currently support function calling (Gemini, Mistral) have a similar problem?

Mistral has the same issue with its streaming API. I will address it in a separate PR. Issue: #6316