Decouple Handlers and Collections from protocol types (#765)

* Decouple Handlers and Collections (e.g. ToolsHandler and ToolsCollection) from Capabilities by promoting them to the options types.

Also, group all handlers in container classes, for server, I decided to move McpServerHandlers down to Mcp.Core and move the NotificationHandlers there too.

Also, Fix ListResourceTemplatesHandler issue.

* Add remarks for empty protocol capability types

* Keep JsonIgnore properties and mark them as Obsolete

* Continue supporting Obsolete members

* Update Obsolete messages to indicate the member will be removed

* Add EditorBrowsable Never to the remaining obsolete members

tests/ModelContextProtocol.AspNetCore.Tests/HttpServerIntegrationTests.cs

@@ -251,9 +251,7 @@ public abstract class HttpServerIntegrationTests : LoggedTest, IClassFixture<Sse
         int samplingHandlerCalls = 0;
 #pragma warning disable CS1998 // Async method lacks 'await' operators and will run synchronously
         McpClientOptions options = new();
-        options.Capabilities = new();
-        options.Capabilities.Sampling ??= new();
-        options.Capabilities.Sampling.SamplingHandler = async (_, _, _) =>
+        options.Handlers.SamplingHandler = async (_, _, _) =>
         {
             samplingHandlerCalls++;
             return new CreateMessageResult