[EN-1454] TimeNanos refactoring

Author: iamishalkin

dxfeed/core/utils/handler.pyx

@@ -103,11 +103,10 @@ cdef class DefaultHandler(EventHandler):
 
 
         df = pd.DataFrame(df_data, columns=self.columns)
-        time_columns = df.columns[df.columns.str.contains('Time')].tolist()
-        nanos = time_columns.pop(time_columns.index('TimeNanos')) if 'TimeNanos' in time_columns else None
+        time_columns = (column for column in df.columns if 'Time' in column and 'TimeNanos' not in column)
         for column in time_columns:
             df.loc[:, column] = df.loc[:, column].astype('datetime64[ms]')
-        if nanos and 'Time' in time_columns:
-            df.loc[:, 'Time'] += df.loc[:, nanos].astype('timedelta64[ns]')
-            df.drop(columns=[nanos], inplace=True)
+        if 'TimeNanos' in df.columns and 'Time' in df.columns:
+            df.loc[:, 'Time'] += df.loc[:, 'TimeNanos'].astype('timedelta64[ns]')
+            df.drop(columns=['TimeNanos'], inplace=True)
         return df