feat: 兼容 Flarum 2.0

- composer.json 约束更新为 ^1.0|^2.0，同时支持 1.x 和 2.0
- RemoveEmailDriver 适配 2.0 ExtenderInterface nullable 类型签名
- 其余 API（Event、Registered、notification.drivers、User::setPreference）2.0 无变化，无需改动
- 已在 2.0 RC1 环境验证通过

composer.json

@@ -4,7 +4,7 @@
     "type": "flarum-extension",
     "license": "MIT",
     "require": {
-        "flarum/core": "^1.0"
+        "flarum/core": "^1.0|^2.0"
     },
     "autoload": {
         "psr-4": {

src/RemoveEmailDriver.php

@@ -8,7 +8,7 @@ use Illuminate\Contracts\Container\Container;
 
 class RemoveEmailDriver implements ExtenderInterface
 {
-    public function extend(Container $container, Extension $extension = null): void
+    public function extend(Container $container, ?Extension $extension = null): void
     {
         $container->extend('flarum.notification.drivers', function (array $drivers) {
             unset($drivers['email']);