Flatten v2 Problems with time-point-specific overrides

[m-philipps]

Implement PEtab v2-compatible functions for:

• v1.core.flatten_timepoint_specific_output_overrides
• v1.core.unflatten_simulation_df

[dweindl]

This is already implemented for amici. I didn't include it here because I thought it's not relevant for any other tool. Do you have another use case?

[m-philipps]

Excellent. I did not see it because I still get the NotImplementedError by the amici PetabImporter and was looking for a way to do it in PEtab, like I would in v1.
Do you think (1) it makes sense to make the Error message from amici point to amici.importers.petab.flatten_timepoint_specific_output_overrides adn (2) to have a wrapper for that function in petab v2 to mimic the interface from v1?