fix: treat java.sql.Timestamp the same java.util.Date during serialization

src/main/java/org/eclipse/yasson/internal/serializer/types/SqlTimestampSerializer.java

diff --git a/src/main/java/org/eclipse/yasson/internal/serializer/types/SqlTimestampSerializer.java b/src/main/java/org/eclipse/yasson/internal/serializer/types/SqlTimestampSerializer.java
index cd29c44..b442538 100644
--- a/src/main/java/org/eclipse/yasson/internal/serializer/types/SqlTimestampSerializer.java
+++ b/src/main/java/org/eclipse/yasson/internal/serializer/types/SqlTimestampSerializer.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, 2025 Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2026 Oracle and/or its affiliates. All rights reserved.
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Public License v. 2.0 which is available at
@@ -18,6 +18,8 @@
 import java.time.temporal.TemporalAccessor;
 import java.util.Locale;
 
+import org.eclipse.yasson.internal.JsonbDateFormatter;
+
 /**
  * Serializer of the {@link Timestamp} type.
  */
@@ -26,25 +28,34 @@
     /**
      * Default Yasson {@link DateTimeFormatter}.
      */
-    private static final DateTimeFormatter DEFAULT_FORMATTER = DateTimeFormatter.ISO_DATE_TIME.withZone(UTC);
+    private static final DateTimeFormatter DEFAULT_DATE_FORMATTER = DateTimeFormatter.ISO_DATE_TIME.withZone(UTC);
 
     SqlTimestampSerializer(TypeSerializerBuilder serializerBuilder) {
         super(serializerBuilder);
     }
 
     @Override
-    protected TemporalAccessor toTemporalAccessor(Timestamp value) {
-        // convert SQL Timestamp into a Instant to unlock TemporalAccessor access
-        return toInstant(value);
-    }
-
-    @Override
     protected Instant toInstant(Timestamp value) {
         return value.toInstant();
     }
 
     @Override
     protected String formatDefault(Timestamp value, Locale locale) {
-        return DEFAULT_FORMATTER.withLocale(locale).format(toInstant(value));
+        return DEFAULT_DATE_FORMATTER.withLocale(locale).format(toInstant(value));
+    }
+
+    @Override
+    protected String formatWithFormatter(Timestamp value, DateTimeFormatter formatter) {
+        return getZonedFormatter(formatter).format(toTemporalAccessor(value));
+    }
+
+    @Override
+    protected String formatStrictIJson(Timestamp value) {
+        return JsonbDateFormatter.IJSON_DATE_FORMATTER.withZone(UTC).format(toTemporalAccessor(value));
+    }
+
+    @Override
+    protected TemporalAccessor toTemporalAccessor(Timestamp value) {
+        return toInstant(value);
     }
 }