Refactor allowInsecure variable declaration (#3736)

- Changed `allowInsecure` from `var` to `val` to ensure immutability.
- Replaced the nullable safe call `settingsStorage?.decodeBool(AppConfig.PREF_ALLOW_INSECURE) ?: false` with `settingsStorage.decodeBool(AppConfig.PREF_ALLOW_INSECURE, false)` for more concise and readable code.
- This ensures `allowInsecure` is always initialized with a default value of `false` in a cleaner and more efficient way.

V2rayNG/app/src/main/kotlin/com/v2ray/ang/util/fmt/Hysteria2Fmt.kt

@@ -15,7 +15,7 @@ import java.net.URI
 object Hysteria2Fmt : FmtBase() {
 
     fun parse(str: String): ServerConfig {
-        var allowInsecure = settingsStorage?.decodeBool(AppConfig.PREF_ALLOW_INSECURE) ?: false
+        val allowInsecure = settingsStorage.decodeBool(AppConfig.PREF_ALLOW_INSECURE,false)
         val config = ServerConfig.create(EConfigType.HYSTERIA2)
 
         val uri = URI(Utils.fixIllegalUrl(str))