Function execute_recursive_cte 

pub fn execute_recursive_cte<E, R>(
    stmt: &RecursiveCteStatement,
    execute_fn: E,
    register_batches_fn: R,
) -> SqlResult<RecursiveCteResult>
where
    E: FnMut(&str) -> SqlResult<Vec<RecordBatch>>,
    R: FnMut(&str, &[RecordBatch]) -> SqlResult<()>,

Execute a recursive CTE using a SqlEngine-like executor callback.

execute_fn is called with a SQL string and the name of the current “working table” (a registered view containing the current accumulator rows). It must return the resulting batches or an error.

register_batches_fn is called to register each iteration’s accumulator as a temporary view under cte_name so the recursive branch can reference it.