Make MinFraudException a sealed class

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: oschwald

src/main/java/com/maxmind/minfraud/exception/InsufficientFundsException.java

@@ -4,7 +4,7 @@
  * This exception is thrown when your account does not have sufficient funds to complete the
  * request.
  */
-public class InsufficientFundsException extends MinFraudException {
+public final class InsufficientFundsException extends MinFraudException {
 
     /**
      * @param message A message explaining the cause of the error.

src/main/java/com/maxmind/minfraud/exception/InvalidRequestException.java

@@ -7,7 +7,7 @@
  * occurs when the web service is up and responding to requests, but the request sent was invalid in
  * some way.
  */
-public class InvalidRequestException extends MinFraudException {
+public final class InvalidRequestException extends MinFraudException {
     private final String code;
     private final int httpStatus;
     private final URI uri;

src/main/java/com/maxmind/minfraud/exception/MinFraudException.java

@@ -7,7 +7,9 @@
  * It also serves as the base class for {@code AuthenticationException},
  * {@code InsufficientFundsException}, and {@code InvalidRequestException}.
  */
-public class MinFraudException extends Exception {
+public sealed class MinFraudException extends Exception
+    permits AuthenticationException, InsufficientFundsException, InvalidRequestException,
+        PermissionRequiredException {
 
     /**
      * @param message A message explaining the cause of the error.