fix: replace raw array access with data_get() to prevent Undefined array key

- Migrate $protocol_settings['key'] to data_get($protocol_settings, 'key') across General, SingBox, Shadowrocket, Surfboard, QuantumultX
- Prevents PHP 8 Undefined array key fatal errors when optional protocol_settings fields are missing
- Same class of bug that caused #735

app/Protocols/Surfboard.php

@@ -89,7 +89,7 @@ class Surfboard extends AbstractProtocol
             "{$server['name']}=ss",
             "{$server['host']}",
             "{$server['port']}",
-            "encrypt-method={$protocol_settings['cipher']}",
+            "encrypt-method=" . data_get($protocol_settings, 'cipher'),
             "password={$password}",
             'tfo=true',
             'udp-relay=true'