Removes final use of deprecated .feasible attribute.

[samgdotson]

This PR addresses a warning I received

../../miniforge3/envs/2025-dotson-thesis/lib/python3.11/site-packages/pymoo/core/individual.py:617: 60100 warnings
  /Users/samdotson/miniforge3/envs/2025-dotson-thesis/lib/python3.11/site-packages/pymoo/core/individual.py:617: DeprecationWarning: The ``feasible`` property for ``pymoo.core.individual.Individual`` is deprecated
    v = getattr(self, key)

This seemed strange since Individual isn't a component of pymoo that I use explicitly. I tracked down the remaining instance of .feasible to replacement.py.

Hopefully, this fully addresses the internal use of .feasible and the attribute can be retired. Though I haven't done that here.

An early attempt to resolve this warning can was from #631, but it missed a spot 😄.