Function check_col_and_build_expr 

fn check_col_and_build_expr<F>(
    span_key: String,
    resource_key: String,
    key: &str,
    col_names: &HashSet<String>,
    expr_builder: F,
) -> Option<Expr>
where
    F: FnOnce(String) -> Expr,

Helper function to check if span_key or resource_key exists in col_names and create an expression. If neither exists, logs a warning and returns None.