Feature description

Add a function that can assess the identifiability of an optimisation result and return an informative message to the user.

Motivation

To help users consider the identifiability of an optimal point.

Possible implementation

Compute a finite difference approximation of the Hessian matrix around the result of an optimisation and classify the eigenvalues.

Additional context

Useful webpage related to this issue: https://sethna.lassp.cornell.edu/Sloppy/WhatAreSloppyModels.html