A Sorted Key-Value Store with Range Queries

Implement SortedStore that keeps keys sorted (using bisect, not re-sorting) and supports:

• put(key, value) (overwrites existing), get(key, default=None), delete(key) (no error if missing)
• range(lo, hi): list of (key, value) with lo <= key < hi, in key order
• floor(key): the largest stored key <= key, or None; ceiling(key): the smallest >= key, or None
• __len__