You are given two 2D integer arrays nums1 and nums2.

Each array contains pairs of the form [id_i, val_i], indicating an identification number id_i and its associated value val_i. Both arrays are sorted in strictly ascending order by their identification numbers and contain unique identification numbers.

Merge the two arrays into a single 2D array sorted in strictly ascending order by id such that:

• Each unique id appears only once in the result.

• If an id is present in only one array, it retains its original value.

• If an id is present in both arrays, its value becomes the sum of the values from both arrays.

Return the merged 2D array.

Constraints:

• $1 \leq$ nums1.length, nums2.length $\leq 200$

• nums1[i].length $=$ nums2[j].length $= 2$

• $1 \leq$ id_i, val_i $\leq 1000$

• Both arrays contain unique id values.

• Both arrays are in strictly ascending order by id.

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