Update default solver for each model to match Vensim's

[natema]

As noted in https://github.com/worlddynamics/WorldDynamics.jl/issues/114#issuecomment-1542412937, the functions running the different scenarios should be update to match the original solver employed in Vensim. We should also document such default solvers somewhere, probably in the page dedicated to each model (e.g. this for World2).