Forecast stamp in the data #31

Hi,

Thank you for the great work on this. I have one suggestion.

I see that you have included IMF forecasts alongside historical data. It would be very helpful to add a dedicated column in the output data indicating when the forecast period begins. This is especially important for public debt series, as the last outturn date might not coincide with the calendar year. For example, if the last observed data point is 2024, any subsequent years in the table are actually forecasts.