Experimental: Bilateral superficial cervical plexus blocks + local wound infiltration

the bilateral superficial cervical plexus block will be performed with 10mL of 0.25% Bupivacaine injected bilaterally (total 20mL) at Erb's point in the lateral neck, which is located at the mid-point between the mastoid process and the posterior border of the clavicular head of the sternocleidomastoid muscle. The injection is just below the lateral border of the sternocleidomastoid muscle, which produces surface level anesthesia of the neck, targeting superficial nerves of the cervical plexus. Then 10mL of 0.25% Bupivacaine will be injected at the planned neck incision (local wound infiltration) on the anterior neck. These will be done intra-operative and only once

Placebo_comparator: placebo + local wound infiltration

10mL of 0.25% bupivacaine injected at the planned neck incision (local wound infiltration), with 10mL of normal saline injected at bilateral Erb's point (total 20mL) (placebo at site of BSCPB). These will be done intra-operative and only once.