Overhaul tool handling (#89)

* Overhaul tool handling

- Renames [McpTool{Type}] to [McpServerTool{Type}], in order to distinguish representations of tools on the server from tools on the client.
- Enables [McpServerTool] methods to have arguments injected from DI, as well as a specific set of types from the implementation directly, like IMcpServer.
- Renames WithTools to WithToolsFromAssembly.
- All of the WithToolsXx methods now publish each individual McpServerTool into DI; other code can do so as well. The options setup code gathers all of the tools from DI and combines them into a collection which is then stored in McpServerOptions and used to construct the server.
- The server tools specified via DI as well as manually-provided handlers, using CallToolHandler as a fallback in case the requested tool doesn't exist in the tools collection, and ListToolsHandler augments the information for whatever tools exist.
- The tools are stored in McpServerOptions in a new McpServerToolCollection type, which is a thread-safe container that exposes add/removal notification. Adding/removing tools triggers a change notification that in turn sends a notification to the client about a tools update.
- The ServerOptions are exposed from the server instance.
- Removed cursor-based APIs from McpClientExtensions.
- Changed McpClientExtensions APIs to return `Task<IList<...>` rather than `IAsyncEnumerable<...>`.

I'm sure this will need to evolve further before we're "done", but it's a significant improvement from where we are now. One area I'm not super happy with is the notifying collection; that might work ok for a stdio server, where you can grab the created collection from the server's options and mutate it, but I don't know how well that's going to work for sse servers.

* Make McpServerTool{Collection} extensible

* Fix README.md example

* Add notifications test

* Address feedback

src/ModelContextProtocol/Utils/Json/McpJsonUtilities.cs

@@ -1,4 +1,5 @@
-using ModelContextProtocol.Protocol.Messages;
+using Microsoft.Extensions.AI;
+using ModelContextProtocol.Protocol.Messages;
 using ModelContextProtocol.Protocol.Types;
 using System.Diagnostics.CodeAnalysis;
 using System.Text.Json;
@@ -62,6 +63,10 @@ public static partial class McpJsonUtilities
             };
         }
 
+        // Include all types from AIJsonUtilities, so that anything default usable as part of an AIFunction
+        // is also usable as part of an McpServerTool.
+        options.TypeInfoResolverChain.Add(AIJsonUtilities.DefaultOptions.TypeInfoResolver!);
+
         options.MakeReadOnly();
         return options;
     }

src/ModelContextProtocol/Utils/SemaphoreSlimExtensions.cs

@@ -0,0 +1,15 @@
+namespace ModelContextProtocol.Utils;
+
+internal static class SynchronizationExtensions
+{
+    public static async ValueTask<Releaser> LockAsync(this SemaphoreSlim semaphore, CancellationToken cancellationToken = default)
+    {
+        await semaphore.WaitAsync(cancellationToken).ConfigureAwait(false);
+        return new(semaphore);
+    }
+
+    public readonly struct Releaser(SemaphoreSlim semaphore) : IDisposable
+    {
+        public void Dispose() => semaphore.Release();
+    }
+}