professional responsibility; disqualification of counsel based on conflicts of interest between former counsel and counsel associated in practice with former counsel; conflict imputation to lawyers associated in practice; Rules 1.6, 1.9, and 1.10 of the North Carolina Rules of Professional Conduct; no appeal of right exists from the denial of a motion to disqualify opposing counsel; trial court did not err, much less abuse its discretion, in denying motion to disqualify based on imputed conflict between former counsel in the same case who became associated in practice with opposing counsel after representation was terminated