Integrate Microsoft.Extensions.AI as a foundational building block (#94)

* Integrate Microsoft.Extensions.AI as a foundational building block

As with logging abstractions coming from M.E.Logging and DI abstractions coming from M.E.DependencyInjection, M.E.AI provides the relevant AI abstractions.

- Adds AsAIFunction and GetAIFunctionsAsync methods for getting functions for tools via a client.
- Uses AIFunctionFactory to implement McpServerBuilderExtensions.WithTools.
- Adds a RequestSamplingAsync overload that accepts ChatMessages/Options.
- Adds an AsSamplingChatClient method that provides an IChatClient usable on the server to request sampling of the client.
- Adds a CreateSamplingHandler method to enable an IChatClient to be easily used to satisfy sampling requests on the client.
- Deprecate McpDotNet.Extensions.AI.

* Address PR feedback

src/mcpdotnet/Protocol/Types/Tool.cs

@@ -1,4 +1,6 @@
-namespace McpDotNet.Protocol.Types;
+using System.Text.Json.Serialization;
+
+namespace McpDotNet.Protocol.Types;
 
 /// <summary>
 /// Represents a tool that the server is capable of calling. Part of the ListToolsResponse.
@@ -9,18 +11,18 @@ public class Tool
     /// <summary>
     /// The name of the tool.
     /// </summary>
-    [System.Text.Json.Serialization.JsonPropertyName("name")]
+    [JsonPropertyName("name")]
     public string Name { get; set; } = string.Empty;
 
     /// <summary>
     /// A human-readable description of the tool.
     /// </summary>
-    [System.Text.Json.Serialization.JsonPropertyName("description")]
+    [JsonPropertyName("description")]
     public string? Description { get; set; }
 
     /// <summary>
     /// A JSON Schema object defining the expected parameters for the tool.
     /// </summary>
-    [System.Text.Json.Serialization.JsonPropertyName("inputSchema")]
+    [JsonPropertyName("inputSchema")]
     public JsonSchema? InputSchema { get; set; }
 }