NewStaticRows created static rows pull executor.

Empty executor.

PullChain combines a sequence of executors in a linked list and exposes them as a single executor.

PullLimit is an executor for LIMIT <offset>, <count> statement and its variations.

PullSort - a simple in memory sort executor TODO this won't work for large resultsets - we need to store in chunks on disk and use a multi-way merge sort in that case.