Merge Two Sorted Lists

Problem: Given two sorted lists, merge them into one.

// 7 ms (Beats 90%)
// 11.15 MB (Beats 32%)

# 54 ms (Beats 96%)
# 17.43 MB (Beats 54%)

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]: