.NET: Add AzureStorageBlob integration as AgentThreadStore support

[DeagleGross]

Motivation and Context

Added a new package, which adds the API to configure AgentThreadStore for AIAgent to use AzureStorageBlob as the agent thread store. It adds persistence of the thread to the application, and makes Hosting packages production-suitable covering persistence.

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.

[DeagleGross]

not sure if we need other API here, but felt like BlobContainerClient is the best option - it allows to set the most granular access to the container itself.

[Copilot]

Pull Request Overview

This PR adds Azure Blob Storage integration for agent thread persistence to the Microsoft Agent Framework. It introduces a new project Microsoft.Agents.AI.Hosting.AzureStorage that provides an implementation of AgentThreadStore using Azure Blob Storage, along with corresponding unit tests.

Key Changes:

• New AzureBlobAgentThreadStore implementation for persisting agent threads to Azure Blob Storage
• Extension methods to configure agents with Azure Blob thread store
• Unit tests with Azurite emulator support for local testing
• CI/CD workflow updates to start Azurite for running tests

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
dotnet/src/Microsoft.Agents.AI.Hosting.AzureStorage/Blob/AzureBlobAgentThreadStore.cs	Core implementation for Azure Blob Storage thread persistence
dotnet/src/Microsoft.Agents.AI.Hosting.AzureStorage/Blob/AzureBlobAgentThreadStoreOptions.cs	Configuration options for the blob store
dotnet/src/Microsoft.Agents.AI.Hosting.AzureStorage/HostedAgentBuilderExtensions.Blob.cs	Extension methods for configuring agents with blob storage
dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/AzureBlobAgentThreadStoreTests.cs	Unit tests for the blob store implementation
dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/TestRunner.cs	Test helper for running agent scenarios
dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/Mock/MockChatClient.cs	Mock chat client for testing
dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/AzureStorageEmulatorAvailabilityHelper.cs	Helper for checking Azurite availability
dotnet/samples/AgentWebChat/AgentWebChat.AgentHost/Program.cs	Sample code demonstrating blob storage usage
.github/workflows/dotnet-build-and-test.yml	CI workflow updated to start Azurite

Comments suppressed due to low confidence (1)

dotnet/tests/Microsoft.Agents.AI.Hosting.AzureStorage.UnitTests/Mock/MockChatClient.cs:28

• This assignment to lastUserMessage is useless, since its value is never read.

        ChatMessage lastUserMessage = messageList.LastOrDefault(m => m.Role == ChatRole.User)
            ?? new ChatMessage(ChatRole.User, "No user message");