Confusing return type in many solvers

For example, in LBFGS


Reading the Return type, it would seem like this returns an object of type OptStep, while in reality, it returns a tuple, of which the second argument is of type OptStep

Start with the LBFGS solver entry point and compare its documented return type with the tuple described in the issue. Inspect the corresponding return documentation or annotations across the other solvers, then verify that each documented return value matches what the solver actually returns.

Written by the indexing model from the issue text.