Fix Decimal64Codec to use unbiased (banking) rounding

Author: plokhotnyuk

jsoniter-scala-macros/jvm/src/test/scala/com/github/plokhotnyuk/jsoniter_scala/macros/JsonCodecMakerDecimal64Spec.scala

@@ -3,20 +3,21 @@ package com.github.plokhotnyuk.jsoniter_scala.macros
 import com.epam.deltix.dfp.{Decimal64, Decimal64Utils}
 import com.github.plokhotnyuk.jsoniter_scala.core._
 import com.github.plokhotnyuk.jsoniter_scala.macros.JsonCodecMaker._
+import java.math.MathContext
 
 class JsonCodecMakerDecimal64Spec extends VerifyingSpec {
   import Decimal64Codec._
 
   "Decimal64Codec" should {
     "deserialize both numeric and string representation of numbers to canonized Decimal64 values" in {
       verifyDeser(make[List[Decimal64]],
-        List(Decimal64.ONE_TENTH, Decimal64.MILLION, Decimal64.fromLong(4503599627370497L), Decimal64.parse("1.23456789e+309"), Decimal64.MAX_VALUE),
-        """[0.1,"001000000",4503599627370497,1.23456789e+309,"9999999999999999e+369"]""")
+        List(Decimal64.ONE_TENTH, Decimal64.MILLION, Decimal64.fromLong(4503599627370497L), Decimal64.parse("1.23456789e+309"), Decimal64.MAX_VALUE, Decimal64.parse("0.12345678901234565")),
+        """[0.1,"001000000",4503599627370497,1.23456789e+309,"9999999999999999e+369",0.12345678901234565]""")
     }
     "serialize Decimal64 values into numeric or string representation depending on number of mantissa bits of canonized in-memory representation" in {
       verifySer(make[List[Decimal64]],
-        List(Decimal64.ONE_TENTH, Decimal64.MILLION, Decimal64.fromLong(4503599627370497L), Decimal64.parse("1.23456789e+309"), Decimal64.MAX_VALUE),
-        """[0.1,1E+6,"4503599627370497","1.23456789E+309","9.999999999999999E+384"]""")
+        List(Decimal64.ONE_TENTH, Decimal64.MILLION, Decimal64.fromLong(4503599627370497L), Decimal64.parse("1.23456789e+309"), Decimal64.MAX_VALUE, Decimal64.parse("0.12345678901234565")),
+        """[0.1,1E+6,"4503599627370497","1.23456789E+309","9.999999999999999E+384",0.1234567890123456]""")
     }
   }
 }
@@ -30,7 +31,7 @@ object Decimal64Codec {
       } else {
         in.rollbackToken()
         in.readBigDecimal(null)
-      }).bigDecimal)))
+      }).bigDecimal.plus(MathContext.DECIMAL64))))
 
     override def encodeValue(x: Decimal64, out: JsonWriter): Unit = {
       val cx = Decimal64Utils.canonize(Decimal64.toUnderlying(x))