unify all JSONRPC stuff into one type

Author: odrobnik

.swiftpm/xcode/xcshareddata/xcschemes/SwiftMCPDemo.xcscheme

@@ -69,7 +69,7 @@
          </CommandLineArgument>
          <CommandLineArgument
             argument = "--token secret"
-            isEnabled = "NO">
+            isEnabled = "YES">
          </CommandLineArgument>
       </CommandLineArguments>
       <EnvironmentVariables>

Sources/SwiftMCP/Models/JSONRPC/ErrorObject.swift

@@ -9,9 +9,9 @@ import Foundation
 import AnyCodable
 
 /// JSON-RPC Request structure used for communication with the MCP server
-public struct JSONRPCMessage: Encodable {
+public struct JSONRPCMessage: Codable {
 
-	public struct Error: Encodable {
+	public struct Error: Codable {
 		public var code: Int
 		public var message: String
 	}
@@ -20,5 +20,7 @@ public struct JSONRPCMessage: Encodable {
 	public var id: Int?
 	public var method: String?
 	public var params: [String: AnyCodable]?
+	public var result: [String: AnyCodable]?
+
 	public var error: Error?
 }