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

samples/ChatWithTools/Program.cs

@@ -41,7 +41,10 @@ var mcpClient = await McpClient.CreateAsync(
     }),
     clientOptions: new()
     {
-        Capabilities = new() { Sampling = new() { SamplingHandler = samplingClient.CreateSamplingHandler() } },
+        Handlers = new()
+        {
+            SamplingHandler = samplingClient.CreateSamplingHandler()
+        }
     },
     loggerFactory: loggerFactory);