Expand InitializeRequestHandler

[TheEterna]

I've noticed that the current InitializeRequestHandler doesn't have any access points, which means it's difficult for the server to perform exclusive initialization operations for different clients. My modification suggestions are as follows:

io.modelcontextprotocol.spec.McpServerSession#handleIncomingNotification

private Mono<Void> handleIncomingNotification(McpSchema.JSONRPCNotification notification) {
		return Mono.defer(() -> {
			if (McpSchema.METHOD_NOTIFICATION_INITIALIZED.equals(notification.method())) {
				this.state.lazySet(STATE_INITIALIZED);
				exchangeSink.tryEmitValue(new McpAsyncServerExchange(this, clientCapabilities.get(), clientInfo.get()));
// modify method signature ，and expose the initNotify Handler for user settings
				return this.exchangeSink.asMono().flatMap(exchange -> this.initNotificationHandler.handle(exchange, notification.params()));

			}

			var handler = notificationHandlers.get(notification.method());
			if (handler == null) {
				logger.error("No handler registered for notification method: {}", notification.method());
				return Mono.empty();
			}
			return this.exchangeSink.asMono().flatMap(exchange -> handler.handle(exchange, notification.params()));
		});
	}