Improve handling of queries beyond the row limit

Previously, we would process a full query until it hit the limit and then just return nothing to the user

https://github.com/cmu-delphi/delphi-epidata/blob/9844600b0de41f7d8e93bfb7d7dff7e0740b0792/src/server/_printer.py#L90-L99

Then I added a LIMIT clause, but in an unintuitive place

https://github.com/cmu-delphi/delphi-epidata/blob/9844600b0de41f7d8e93bfb7d7dff7e0740b0792/src/server/_query.py#L238-L248

• The LIMIT addition should probably be in the QueryBuilder object.
• The row counting might be obsolete since the LIMIT query should handle that (cc @melange396 to confirm). Update: the row counting in the printer is needed when dealing with multiple SQL queries; interestingly, these are only used in non-covidcast endpoints
• run_query probably doesn't need the p: APrinter then.