Find the Length of the Longest Common Prefix

Given two arrays of positive integers, return the maximum length (in digits) of a common leftmost-digit prefix shared by any number from arr1 and any number from arr2, or 0 if none exists. The core task is efficiently comparing digit-prefixes across up to 5e4 numbers (digits ≤9), e.g., by converting to strings and using prefix sets, tries, or hashing to find the longest intersecting prefix.