Fix CS0234: The type or namespace name 'Ext' does not exist in the namespace 'Oxide'

using System;
using System.Collections.Generic;
using Newtonsoft.Json;

namespace Oxide.Plugins
{
    [Info("DiscordReport", "RustPluginGenerator", "1.0.0")]
    [Description("Sends a short status report to a Discord channel via webhook")]
    public class DiscordReport : RustPlugin
    {
        private PluginConfig config;

        private class PluginConfig
        {
            [JsonProperty("Discord webhook URL")]
            public string WebhookUrl = "";

            [JsonProperty("Broadcast report")]
            public bool Broadcast = false;
        }

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null)
                {
                    throw new Exception();
                }
            }
            catch
            {
                PrintWarning("Configuration file is invalid, using defaults");
                LoadDefaultConfig();
            }
            SaveConfig();
        }

        protected override void SaveConfig() => Config.WriteObject(config);

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["ReportQueued"] = "Report queued.",
                ["ReportLine"] = "Online players: {0} | Reporter: {1}",
                ["Broadcast"] = "{0}"
            }, this);
        }

        private string Msg(string key, string userId = null, params object[] args) => string.Format(lang.GetMessage(key, this, userId), args);

        private void OnServerInitialized()
        {
            Puts("DiscordReport loaded");
        }

        [ChatCommand("report")]
        private void CmdReport(BasePlayer player, string command, string[] args)
        {
            if (player == null)
            {
                return;
            }

            int online = BasePlayer.activePlayerList.Count;
            string text = Msg("ReportLine", player.UserIDString, online, player.displayName);

            if (config.Broadcast)
            {
                Server.Broadcast(Msg("Broadcast", null, text));
            }

            // Discord extension is not available; log the report on the server instead.
            Puts("[DiscordReport] " + text);
            if (!string.IsNullOrEmpty(config.WebhookUrl))
            {
                timer.Once(0.1f, () => Puts("[DiscordReport] Webhook configured but the Discord extension is not loaded: " + config.WebhookUrl));
            }

            SendReply(player, Msg("ReportQueued", player.UserIDString));
        }
    }
}