Given an input string and a list of relevance scores, find the most relevant contiguous subarray.
The string and scores have equal length. Return the contiguous substring selected by the scoring rules: if the total score is nonnegative, return the complete string; otherwise, return the highest-scoring contiguous segment. If every score is negative, return the right-middle character.
Implement most_relevant_subarray(text, scores). Return a string. The input string is non-empty, and scores[i] corresponds to text[i].
def most_relevant_subarray(text, scores):