Fix Query constructor to return error for dense arrays with return_incomplete=True

[kounelisagis]

Incomplete queries are only supported for sparse arrays in TileDB-Py at this time. Dense reads will internally reallocate buffers and resubmit the query until successful completion. Docs: https://docs.tiledb.com/main/how-to/arrays/reading-arrays/incomplete-queries

Additionally, create a test to verify the expected behavior for both sparse and dense arrays.