“An allegation of judicial bias should not be made lightly because, by definition, it challenges the integrity of the judge in relation to the core of the judicial function – to preside impartially over the case before the judge: see R. v. S.(R.D.), 1997 CanLII 324 (SCC), [1997] 3 S.C.R. 484, at paras. 31-32.”