Given an integer array arr and an integer k, find the maximum subarray sum in the array obtained by concatenating arr k times.

The subarray can be empty, which corresponds to a sum of $0$.

Since the answer may be very large, return the result modulo $10^9 + 7$.

Constraints:

• $1 \leq$ arr.length $\leq 10^5$

• $1 \leq$ k $\leq 10^5$

• $-10^4 \leq$ arr[i] $\leq 10^4$

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