Prepare worker for use with the new gateway

[kalabukdima]

This PR changes the output format of the query results, i.e., of the data field.

• The result is written in the JSON lines format instead of a single JSON array. Rationale can be found here.
• The result is limited in size to fit in the allowed transport message limit.
• The last included block is returned to simplify forming a follow-up request.
• The block range is passed separately from the query body.