refactor(snapbi): address PR feedback and add fixture-based webhook tests

- Apply Copilot suggestions: @OverRide on getMessage(), StandardCharsets.UTF_8
  in test helper, remove redundant toLowerCase(), fix CHANGELOG grammar
- Restore minifyJson to private visibility, test through public API only
- Replace direct minifyJson unit tests with fixture-based webhook signature
  tests covering VA, QRIS, and Direct Debit (pending + success/settlement)
- Add JSON fixture files with edge cases: spaces in string values, escaped
  quotes, empty objects, nested arrays

Author: salismidtrans

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ## v3.2.2 (April 7, 2026)
 
-Bugs fix:
+Bug fixes:
 - Fix `minifyJson()` in SnapBi stripping whitespace inside JSON string values, which caused incorrect SNAP-BI webhook notification signature verification. The method now uses a character-level JSON minifier that preserves whitespace within quoted strings.
 - Fix `MidtransError` getter methods not being generated by Lombok on JDK 25. Replaced `@Getter` annotation with explicit getter methods for `statusCode`, `responseBody`, and `response`.
 

library/src/main/java/com/midtrans/httpclient/error/MidtransError.java

@@ -12,6 +12,7 @@ public class MidtransError extends Exception {
     private String responseBody;
     private Response response;
 
+    @Override
     public String getMessage() {
         return message;
     }

library/src/main/java/com/midtrans/snapbi/SnapBi.java

@@ -294,7 +294,7 @@ public static String getSymmetricSignatureHmacSh512(String accessToken, Map<Stri
         }
     }
 
-    static String minifyJson(String json) {
+    private static String minifyJson(String json) {
         if (json == null || json.isEmpty()) {
             return "";
         }