Implemented most of ydb_ets_reader.
- Can create an ets table with start_link/3.
- Add tuples to the table with add_tuples/2.
- Send a stream of ydb_tuples to the specified pid with get_data_stream/2.

Tuples of the form {ydb_tuple, 123, {data, data2}} are stored as {{op, 1}, ydb_tuple, 123, {data, data2}}
Fixed dialyzer errors in ydb_ets_reader.