1669. Merge In Between Linked Lists

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1669. Merge In Between Linked Lists
@param {import('../../lib/list-node.js').ListNode | null} list1
@param {number} a
@param {number} b
@param {import('../../lib/list-node.js').ListNode | null} list2
@returns {import('../../lib/list-node.js').ListNode | null}