Raised minSdk to 24，Drop legacy Android support

Raised minSdk to 24 and removed conditional code for pre-Nougat Android versions. Cleaned up context wrapping, notification, and service start logic to use modern APIs. Also removed unnecessary @RequiresApi annotations and legacy feature declarations from the manifest.

V2rayNG/app/build.gradle.kts

@@ -10,10 +10,10 @@ android {
 
     defaultConfig {
         applicationId = "com.v2ray.ang"
-        minSdk = 21
+        minSdk = 24
         targetSdk = 36
         versionCode = 684
-        versionName = "1.10.32"
+        versionName = "1.10.33"
         multiDexEnabled = true
 
         val abiFilterList = (properties["ABI_FILTERS"] as? String)?.split(';')