Chore: seniority in geminals in cc folder

[kzsigmond]

Describe the task or issue:

AP1roG does not set the seniority parameter in fanpy/wfn/cc/pccd_ap1rog.py to 0, like fanpy/wfn/geminal/ap1rog.py does. Similarly hard coding the seniority may not be the best way forward, as other geminals inherit from pCCD.
The BaseCI wavefunction implements the seniority keyword as follows:

    @property
    def seniority(self):
        """Return the seniority of the wavefunction.

        Seniority of a Slater determinant is its number of unpaired electrons. The seniority of the
        wavefunction is the expected number of unpaired electrons.

        Returns
        -------
        seniority : int
            Seniority of the wavefunction.

        Notes
        -----
        `None` means that all possible seniority are allowed.

        """
        return self._seniority

where each subclass can set or modify _seniority or def seniority.