ERROR: no binary output function available for type theta_sketch

```
PostgreSQL 15.7
Citus 12.1.-1
datasketches 1.6.0

select version();
version
---------------------------------------------------------------------------------------------------------
PostgreSQL 15.7 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44), 64-bit

```

```
select report_date, campaign_id, theta_sketch_get_estimate(theta_sketch_union(reach))
from
(select report_date,campaign_id, theta_sketch_union(reach_ds) as reach
from report_day where service_account_id='599267'
group by report_date, campaign_id,representative_id
) a
group by report_date, campaign_id
order by campaign_id, report_date
limit 10;

ERROR: 42883: no binary output function available for type theta_sketch
CONTEXT: while executing command on postgres-citus09:5432
LOCATION: ReportResultError, remote_commands.c:324
Time: 1248.635 ms (00:01.249)
```

Hi.

When using parallel aggregate functions on distributed tables in Citus, an error occurs as seen in 'explain analyze'. However, if I run a query without an analyze or use only 'explain', it works fine.

Riproduci la query SQL segnalata con EXPLAIN ed EXPLAIN ANALYZE su PostgreSQL 15.7, Citus 12.1 e datasketches 1.6.0, quindi confronta i percorsi di aggregazione parallela. Verifica dove viene serializzato il risultato di theta_sketch per l’esecuzione distribuita; il lavoro è completato quando la query analizzata termina senza l’errore binary-output-function.

Scritto dal modello di indicizzazione a partire dal testo della issue.