feat(sql): run a statement in one round trip with execute_query - #4169

execute_query_async is currently the only way to run SQL, and it always submits then fetches — PollFlightInfo so the client learns a ticket encoding and a schema, then DoGet to read the rows. SELECT 1 pays two round trips and two server plans for a handle it never polls, never cancels, and reads once.

Connection::execute_query sends the statement as the ticket and streams the answer on the same call:

let mut batches = db.execute_query("SELECT * FROM events LIMIT 10").execute().await?;

Neither thing the extra round trip was buying is needed. The ticket encoding is nothing the client has to be told, and a DoGet stream carries its schema in its first message rather than in an earlier reply. This is the same shape ClickHouse's Arrow Flight server accepts, where DoGet takes "a raw SQL query string as the ticket value".

Which to use

The async path is unchanged and stays the right tool for a large or slow answer. The new call is the one to reach for otherwise, and the doc comments on each now say so.

Compatibility

Additive. A server that does not read a raw ticket as a statement never sees one unless a caller asks for it by name.

Tests

• One-shot returns the rows and makes zero PollFlightInfo calls with exactly one DoGet — the counters are the real assertion, since a reintroduced planning round trip would still return correct rows.
• An empty result still yields a schema, which the stream is built from before any row is seen.