Given a circular integer array `nums` of length `n`, return the maximum possible sum of a non-empty subarray of `nums`.

A circular array means the end of the array connects to the beginning of the array. Formally, the next element of `nums[i]` is `nums[(i + 1) % n]` and the previous element of `nums[i]` is `nums[(i - 1 + n) % n]`.

A subarray may only include each element of the fixed buffer `nums` at most once. Formally, for a subarray `nums[i], nums[i + 1], ..., nums[j]`, there does not exist `i <= k1`, `k2 <= j` with `k1 % n == k2 % n`.

Example 1:

    Input: nums = [1,-2,3,-2]
    Output: 3
    Explanation: Subarray [3] has maximum sum 3.

Example 2:

    Input: nums = [5,-3,5]
    Output: 10
    Explanation: Subarray [5,5] has maximum sum 5 + 5 = 10.

Example 3:

    Input: nums = [-3,-2,-3]
    Output: -2
    Explanation: Subarray [-2] has maximum sum -2.

Constraints:

- `n == nums.length`
- `1 <= n <= 3 * 104`
- `-3 * 104 <= nums[i] <= 3 * 104`