Refactor group tab to ViewPager2 with fragments

Replaces the group tab and server list RecyclerView in MainActivity with a ViewPager2-based implementation using fragments. Adds GroupPagerAdapter and GroupServerFragment for per-group server lists, introduces BaseFragment for fragment view binding, and updates related logic in MainViewModel and SettingsChangeManager. Updates dependencies to include ViewPager2 and Fragment KTX, and modifies layouts to support the new structure.

V2rayNG/app/build.gradle.kts

@@ -148,6 +148,8 @@ dependencies {
     implementation(libs.preference.ktx)
     implementation(libs.recyclerview)
     implementation(libs.androidx.swiperefreshlayout)
+    implementation(libs.androidx.viewpager2)
+    implementation(libs.androidx.fragment)
 
     // UI Libraries
     implementation(libs.material)