refactor: Optimised codes.

Move all private or protected to the last of files.

property-guard-spring-boot-starter/src/main/java/cn/org/codecrafters/propertyguard/autoconfiguration/PropertyGuard.java

@@ -70,8 +70,6 @@ import java.util.Optional;
  */
 public class PropertyGuard implements EnvironmentPostProcessor {
 
-    private final String PREFIX = "pg";
-
     /**
      * Process the encryption environment variables.
      *
@@ -108,4 +106,6 @@ public class PropertyGuard implements EnvironmentPostProcessor {
             }
         }
     }
+
+    private static final String PREFIX = "pg";
 }