Function is_substring

fn is_substring(x: &[&str], k: &[&str]) -> bool

Determines if each string in one slice occurs as a substring within the corresponding string in another slice.

Compares elements from two slices pairwise, returning true only if every element from the first slice is contained within its matching element in the second slice. The function uses an iterator to zip through both slices and applies the substring check to each pair, ensuring that the condition holds across all compared pairs.