/**
 * Get the count of the longest repeating streak of `substring` in `value`.
 *
 * @param {string} value
 *   Content to search in.
 * @param {string} substring
 *   Substring to look for, typically one character.
 * @returns {number}
 *   Count of most frequent adjacent `substring`s in `value`.
 */
export function longestStreak(value: string, substring: string): number