Use BigDecimal.compareTo instead of string comparison in packBigDecimal

Replace the string-based lossy check with `decimal.compareTo(BigDecimal.valueOf(doubleValue)) != 0`,
avoiding two stripTrailingZeros + toEngineeringString allocations per BigDecimal write.

Author: komamitsu

msgpack-jackson3/src/main/java/org/msgpack/jackson/dataformat/MessagePackGenerator.java

@@ -433,8 +433,7 @@ private void packBigDecimal(BigDecimal decimal)
 
         if (failedToPackAsBI) {
             double doubleValue = decimal.doubleValue();
-            if (!decimal.stripTrailingZeros().toEngineeringString().equals(
-                    BigDecimal.valueOf(doubleValue).stripTrailingZeros().toEngineeringString())) {
+            if (decimal.compareTo(BigDecimal.valueOf(doubleValue)) != 0) {
                 throw new IllegalArgumentException("MessagePack cannot serialize a BigDecimal that can't be represented as double. " + decimal);
             }
             messagePacker.packDouble(doubleValue);

msgpack-jackson3/src/test/java/org/msgpack/jackson/dataformat/MessagePackGeneratorTest.java

@@ -351,6 +351,29 @@ public void testBigDecimal()
         }
     }
 
+    @Test
+    public void testBigDecimalCompareTo()
+            throws IOException
+    {
+        ObjectMapper mapper = new MessagePackMapper(new MessagePackFactory());
+
+        // BigDecimal with trailing zeros is representable as double — must not throw
+        BigDecimal trailingZeros = new BigDecimal("1.50");
+        byte[] bytes = mapper.writeValueAsBytes(trailingZeros);
+        MessageUnpacker unpacker = MessagePack.newDefaultUnpacker(bytes);
+        assertEquals(1.5, unpacker.unpackDouble(), 0.0);
+
+        // BigDecimal with precision beyond double range must throw
+        BigDecimal tooHighPrecision = new BigDecimal("1.00000000000000000000000000000000000001");
+        try {
+            mapper.writeValueAsBytes(tooHighPrecision);
+            assertTrue(false);
+        }
+        catch (IllegalArgumentException e) {
+            assertTrue(true);
+        }
+    }
+
     @Test
     public void testEnableFeatureAutoCloseTarget()
             throws IOException