.NET: Update to latest MEAI 10.0.1 and OpenAI 2.7.0

[Stephen Toub (stephentoub)]

No description provided.

[Copilot]

Pull request overview

This PR updates the Microsoft.Extensions.AI packages from version 10.0.0 to 10.0.1 and OpenAI from 2.6.0 to 2.7.0, adapting the codebase to handle breaking changes in how continuation tokens are typed in the updated MEAI library.

Key Changes:

• Updated package versions for Microsoft.Extensions.AI ecosystem and OpenAI SDK
• Added type casts (as ResponseContinuationToken) in production code to handle the change from object? to ResponseContinuationToken? in MEAI's ChatOptions, ChatResponse, and ChatResponseUpdate
• Updated unit tests to create proper ResponseContinuationToken instances using ResponseContinuationToken.FromBytes() instead of new object()

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
dotnet/Directory.Packages.props	Updated package versions for Microsoft.Extensions.AI (10.0.0 → 10.0.1), Microsoft.Extensions.AI.OpenAI, OpenAI (2.6.0 → 2.7.0), System.ClientModel (1.8.0 → 1.8.1), and Azure.AI.Projects.OpenAI
dotnet/src/Microsoft.Agents.AI/ChatClient/ChatClientAgent.cs	Added type cast to ResponseContinuationToken when assigning continuation token from AgentRunOptions to ChatOptions
dotnet/src/Microsoft.Agents.AI.Abstractions/AgentRunResponseExtensions.cs	Added type casts to ResponseContinuationToken when creating ChatResponse and ChatResponseUpdate from agent run responses
dotnet/tests/Microsoft.Agents.AI.UnitTests/ChatClient/ChatClientAgentTests.cs	Updated test setup to create ResponseContinuationToken instances using FromBytes() instead of creating plain objects
dotnet/tests/Microsoft.Agents.AI.Abstractions.UnitTests/AgentRunResponseUpdateTests.cs	Updated test to create ResponseContinuationToken instance using FromBytes() method