Avoid rebuild if OCV unaffected by parameters

[NicolaCourtier]

Feature description

Rebuild the model for a specified initial_state only if the OCV relationship is affected by the fitting parameters. Such parameters would include those that affect the stoichiometric limits and possibly degradation parameters.

Motivation

To speed up optimisations which don't require a model rebuild.

Possible implementation

Similar to the geometric_parameters?

Additional context

Should be tackled after #444.