- Explain in more details [AD backends](https://control-toolbox.org/OptimalControl.jl/dev/manual-solve.html#manual-solve-direct-method) in the documentation. What do optimized, manual and default and when choosing one or another. - Maybe replace `adnlp_backend` by `adnlp_ad_backend`.
adnlp_backendbyadnlp_ad_backend.