Function validate_no_streaming_subqueries 

pub fn validate_no_streaming_subqueries(
    sql: &str,
    streaming_tables: &HashSet<String>,
) -> SqlResult<()>

Validate that sql contains no subqueries that reference a streaming table.

Returns Ok(()) when either:

• No subqueries are present, or
• No subquery body references a name in streaming_tables.

Returns Err when a subquery body contains a streaming table name (case- insensitive), because DataFusion’s decorrelation rules do not handle unbounded inputs.