Copper(I)−Dioxygen Reactivity of (L)CuI+ (L = Tris(2-pyridylmethyl)amine): Kinetic/Thermodynamic and Spectroscopic Studies Concerning the Formation of Cu−O2 and Cu2−O2 Adducts as a Function of Solvent Medium and 4-Pyridyl Ligand Substituent Variations