[CDC] Do not lose presition during float/double to json serialization… (#7740)

Author: dcherednik

ydb/core/tx/datashard/change_record_cdc_serializer.cpp

@@ -85,10 +85,16 @@ class TJsonSerializer: public TBaseSerializer {
     friend class TChangeRecord; // used in GetPartitionKey()
 
     static NJson::TJsonWriterConfig DefaultJsonConfig() {
-        NJson::TJsonWriterConfig jsonConfig;
-        jsonConfig.ValidateUtf8 = false;
-        jsonConfig.WriteNanAsString = true;
-        return jsonConfig;
+        constexpr ui32 doubleNDigits = std::numeric_limits<double>::max_digits10;
+        constexpr ui32 floatNDigits = std::numeric_limits<float>::max_digits10;
+        constexpr EFloatToStringMode floatMode = EFloatToStringMode::PREC_NDIGITS;
+        return NJson::TJsonWriterConfig {
+            .DoubleNDigits = doubleNDigits,
+            .FloatNDigits = floatNDigits,
+            .FloatToStringMode = floatMode,
+            .ValidateUtf8 = false,
+            .WriteNanAsString = true,
+        };
     }
 
 protected: