Write a generator for substring pattern matches

## Problem Write a generator that scans a string and emits a value whenever a substring matches a given pattern. ### Input - A string `s` - A string `pattern` (non-empty) ### Output Return a generator/iterator that yields `True` **once for each occurrence** of `pattern` in `s`, scanning from left to right. Matches may overlap. ### Examples - `s = "aaaa"`, `pattern = "aa"` → yields `True` 3 times (matches at indices 0, 1, 2) - `s = "abc"`, `pattern = "d"` → yields nothing ### Constraints - `0 <= len(s) <= 10^6` - `1 <= len(pattern) <= 10^5` ### Notes - The solution should avoid quadratic time in the worst case.