6-tert-Butyl-2-(3-{5-[6-(2-dimethylamino-1,1-dimethyl-ethoxy)-pyridazin-3-ylamino]-1-methyl-6-oxo-1,6-dihydro-pyridazin-3-yl}-2-hydroxymethyl-phenyl)-8-fluoro-2H-phthalazin-1-one