cursor method
Set the cursor for keyset pagination. The map is a unique-key value
(e.g. {'id': 'abc'}); the compiler derives a keyset predicate from it
and the current orderBy. Inclusive of the cursor row — pair with
skip(1) to exclude it, matching Prisma.
Implementation
JsonQueryBuilder cursor(Map<String, dynamic> cursor) {
_cursor = cursor;
return this;
}