Make schema agreement example exercise manual waiting

[dkropachev]

The schema-agreement example leaves automatic schema-agreement waiting enabled while also demonstrating a manual wait.

Code permalink:

scylla-rust-driver/examples/schema_agreement.rs

Line 16 in e04a12a

let session: Session = SessionBuilder::new()

Schema-changing queries already await schema agreement by default, so if the create statement times out the example exits before the manual wait, and if it succeeds the manual wait checks an already-agreed schema. That makes the timeout branch misleading for the behavior the example is trying to show.

Suggested direction: disable automatic schema-agreement waiting for this example, or remove the manual timeout handling.