Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 10. A Water-Soluble Bimetallic (Zn II /Pt II ) Porphyrazine Hexacation as Potential Plurimodal Agent for Cancer Therapy: Exploring the Behavior as Ligand of Telomeric DNA G-Quadruplex Structures