In a linked list with an even number of nodes ($n$), each node at position $i$ (using $0$$-$based indexing) is paired with the node at position ($n - 1 - i$). These pairs are called twins for all $0 ≤ i < n/2$.

For example, if $n = 4$, the twin pairs are:

• The node at index $0$ pairs with the node at index $3$.

• The node at index $1$ pairs with the node at index $2$.

The twin sum is the sum of a node’s value and its twin’s value. Given the head of a linked list with an even number of nodes, return the maximum twin sum among all pairs.

Constraints:

• The list contains an even number of nodes in the range $[2, 10^3]$.

• $1 \leq$ Node.value $\leq 10^3$