feat: add leetcode problem 88

[richvigorito]

Description of Change

Leetcode 88:

We use three pointers:

i at the last valid element of nums1 (m - 1),
j at the last element of nums2 (n - 1),
k at the last total index of the merged array (m + n - 1).

References

Checklist

• Added description of change
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• Added tests and example, test must pass. SEE: link
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Notes: