Idea: add functionality to extract values along a contour

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In https://github.com/cfs-energy/cfspopcon/blob/main/cfspopcon/point_selection.py there is the possibility of calculating the coordinates maximizing or minimizing some function.

Could use something like https://github.com/cfs-energy/cfspopcon/blob/separatrix_operational_space/cfspopcon/formulas/separatrix_operational_space/LH_transition_power.py#L13 to extract points along a contour.

Would be an interesting way of setting a constraint (i.e. P_aux = 25MW) and then seeing the relationship between other variables.

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Completed: code available in https://github.com/cfs-energy/cfspopcon/blob/main/cfspopcon/shaping_and_selection/line_selection.py