Refactor and update types and handlers

- README changes: removed 'as const' annotation and note.
- Connector changes: dispatched event for commands in gateway.
- Updated processor type guard for command handlers.
- Removed readonly from CommandHandler types in handler definitions.
- Test adjustments: updated demo tests to reliable command registration.

testing/demo.test.ts

@@ -62,7 +62,7 @@ client.applicationCommands.register('hello', ApplicationCommandType.Chat, create
                 { name: "Bear", value: "Bear" }
             ]
         }
-    ] as const,
+    ],
     execute: async (context, args) => {
         context.reply(
             `\