Improve Import/Export Simulation Errors

[jackzampolin]

Currently errors coming out of the simulator are not very actionable.

cc @fedekunze

[alexanderbez]

Can you elaborate a bit more on this @jackzampolin and @fedekunze? What do we want to see here? We already print the stacktrace. What more should we print or show as output?

[fedekunze]

I think this is particularly the case for the ImportExport simulation. My idea was to Unmarshal the values to the respective types/interfaces in case there're unequal stores. We can do this by reading the key's prefix bytes to identify the respective type.