execute functions to return responses, so return values can get validated by the workload

[fruch]

While try to play around with latte, I was looking on how can I add data validation to a workflow,
and I've found the execute functions are always return empty/nil/unit

    /// Executes an ad-hoc CQL statement with no parameters. Does not prepare.
    pub async fn execute(&self, cql: &str) -> Result<(), CassError> {
        let start_time = self.stats.try_lock().unwrap().start_request();
        let rs = self.session.query(cql, ()).await;
        let duration = Instant::now() - start_time;
        self.stats
            .try_lock()
            .unwrap()
            .complete_request(duration, &rs);
        rs.map_err(|e| CassError::query_execution_error(cql, &[], e))?;
        Ok(())
    }

    /// Executes a statement prepared and registered earlier by a call to `prepare`.
    pub async fn execute_prepared(&self, key: &str, params: Value) -> Result<(), CassError> {
        let statement = self
            .statements
            .get(key)
            .ok_or_else(|| CassError(CassErrorKind::PreparedStatementNotFound(key.to_string())))?;
        let params = bind::to_scylla_query_params(&params)?;
        let start_time = self.stats.try_lock().unwrap().start_request();
        let rs = self.session.execute(statement, params.clone()).await;
        let duration = Instant::now() - start_time;
        self.stats
            .try_lock()
            .unwrap()
            .complete_request(duration, &rs);
        rs.map_err(|e| CassError::query_execution_error(statement.get_statement(), &params, e))?;
        Ok(())
    }

so in cases the query works but comes out empty, latte consider is as correct, while I would like to be able to consider it as
error, and maybe even stop the workflow cause of that

[fruch]

me and @vponomaryov are playing with a bit of different approach, that we would feed into the execute the expectations, to begin with the expecation of how many row we expect of this query, and later down the road to pass a whole row (or part of it), for comparing.

first part is merged in our fork:
scylladb#60

and we are currently experimenting with it when testing tombstone behavior (i.e. deletions/range deletions and such)