This pull request introduces several updates to the solution and package management, as well as minor improvements to the codebase. Notably, it adds two new plugin projects, updates and reorganizes NuGet package dependencies, and enhances metadata handling in conversation models.

Key changes:

Solution and Project Structure:

• Added two new plugin projects: BotSharp.Plugin.MMPEmbedding and BotSharp.Plugin.Membase to the solution, including their build configurations and solution folder assignments. [1] [2] [3]
• Removed the UnitTest project from the solution and its build configurations. [1] [2] [3]
• Updated the Visual Studio version for the solution to 18.0.

NuGet Package Management:

• Updated various package versions, including major updates to System.ClientModel, Azure.AI.OpenAI, OpenAI, Rougamo.Fody, DistributedLock.Redis, and EntityFrameworkCore.BootKit, and added the Polly package. [1] [2] [3] [4] [5] [6]
• Reorganized package references for Microsoft.Extensions.*, System.Text.Json, and Serilog.Extensions.* to ensure correct versions and compatibility across target frameworks. [1] [2] [3]
• Removed direct package references in BotSharp.Abstraction.csproj that are now managed via centralized Directory.Packages.props.

Build and Target Frameworks:

• Changed TargetFramework and LangVersion in BotSharp.AppHost.csproj and BotSharp.ServiceDefaults.csproj to use properties, improving flexibility for multi-targeting. [1] [2]

Conversation Model Enhancements:

• Added a MetaData dictionary property to both DialogMetaData and RoleDialogModel for storing additional metadata in conversation messages. [1] [2]
• Reordered properties in RoleDialogModel.From to match the new property organization.

Codebase Improvements:

• Added the [DebuggerStepThrough] attribute to the Agent class to improve debugging experience by skipping over this class in the debugger.