improve query client

lib/gat/modes/pgbouncer/pools.go

lib/gat/pool/pool.go

lib/gsql/client.go

lib/gsql/eq.go

lib/gsql/errors.go

lib/gsql/query.go

lib/gsql/query_test.go

lib/gsql/result.go

lib/gsql/row.go

lib/psql/reader.go