A comparison of postoperative analgesic efficacy of opioid-free anesthesia using intravenous paracetamol (15 mg/kg), lignocaine (2 mg/kg), and magnesium sulfate (20 mg/kg) versus standard opioid anesthesia using intravenous tramadol (2 mg/kg) for preemptive analgesia in abdominal surgeries under general anesthesia