.NET: Add AsIChatClientWithStoredOutputDisabled for ProjectResponsesClient

[rogerbarreto]

Motivation and Context

Azure AI consumers using ProjectResponsesClient (from Azure.AI.Extensions.OpenAI) had no direct way to disable server-side response storage without taking a dependency on the Microsoft.Agents.AI.OpenAI package. The existing AsIChatClientWithStoredOutputDisabled() extension only targeted the base ResponsesClient type in the OpenAI package.

This change adds a matching extension method for ProjectResponsesClient in the Microsoft.Agents.AI.AzureAI package, enabling Azure AI consumers to disable server-side storage natively.

Description

New extension method:

• ProjectResponsesClientExtensions.AsIChatClientWithStoredOutputDisabled() in Azure.AI.Extensions.OpenAI namespace
• Mirrors the existing ResponsesClient extension from the OpenAI package
• Sets StoredOutputEnabled = false on CreateResponseOptions
• Preserves/wraps any existing RawRepresentationFactory configuration (e.g., model defaults from AsIChatClient)
• Includes ReasoningEncryptedContent by default for stateless multi-turn conversations
• Optional deploymentName parameter (model is no longer required since AsIChatClient() accepts optional model)
• Experimental attributes match existing OpenAI counterpart: [Experimental(OPENAI001)] on class, [Experimental(MAAI001)] on method

Doc fix:

• Updated OpenAIResponseClientExtensions.AsIChatClientWithStoredOutputDisabled doc to remove "Required when using a plain ResponsesClient" for the model parameter

Tests:

• 6 new unit tests in Microsoft.Agents.AI.AzureAI.UnitTests covering:
  • Null guard (ArgumentNullException)
  • Inner client accessibility via GetService<ResponsesClient>()
  • StoredOutputEnabled = false with reasoning encrypted content (default)
  • Explicit includeReasoningEncryptedContent: true
  • includeReasoningEncryptedContent: false excludes reasoning content
  • Optional deploymentName parameter
• Test helper uses reflection over _configureOptions field, matching the existing pattern in OpenAIResponseClientExtensionsTests

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

Adds a ProjectResponsesClient-specific AsIChatClientWithStoredOutputDisabled extension so Azure AI consumers can disable server-side response storage without taking a dependency on Microsoft.Agents.AI.OpenAI, plus adds unit tests and adjusts related XML docs.

Changes:

• Added ProjectResponsesClientExtensions.AsIChatClientWithStoredOutputDisabled(...) in Azure.AI.Extensions.OpenAI.
• Added unit tests validating null-guarding, service chain access, and CreateResponseOptions settings.
• Updated XML doc text for the existing OpenAIResponseClientExtensions method parameter description.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
dotnet/tests/Microsoft.Agents.AI.AzureAI.UnitTests/ProjectResponsesClientExtensionsTests.cs	Adds unit tests for the new extension behavior and configuration.
dotnet/src/Microsoft.Agents.AI.OpenAI/Extensions/OpenAIResponseClientExtensions.cs	Tweaks XML docs to remove potentially outdated “required model” wording.
dotnet/src/Microsoft.Agents.AI.AzureAI/ProjectResponsesClientExtensions.cs	Introduces the new extension method for ProjectResponsesClient to disable stored output and optionally include reasoning encrypted content.