On the excitonic effects of the 1T and 1O <math display='"inline"' id='"d1e1203"' altimg='"si73.svg"'> <msub> <mrow></mrow> <mrow> <mi mathvariant='"normal"'>T</mi> </mrow> </msub> </math> phases of PdS2, PdSe2, and PdSSe monolayers