Status: IN
Deletion is represented by writing a record with an empty-string value; both `_scan_data_file` (checks `val_size == 0`) and `get` (checks `value == ""`) use this convention.
Source: entries/2026/05/28/hash-index-storage-bitcask.md
TOMBSTONE = b"__BITCASK_TOMBSTONE__"
def delete(self, key):
self._write_record(key, TOMBSTONE)