Refactor projection initialization in PyDataFrame to improve clarity

Author: kosiew

src/dataframe.rs

@@ -59,6 +59,7 @@ use crate::{
     expr::{sort_expr::PySortExpr, PyExpr},
 };
 
+#[allow(clippy::manual_c_str_literals)]
 static ARROW_STREAM_NAME: &CStr =
     unsafe { CStr::from_bytes_with_nul_unchecked(b"arrow_array_stream\0") };
 
@@ -946,7 +947,7 @@ impl PyDataFrame {
         let stream = spawn_stream(py, async move { df.execute_stream().await })?;
 
         let mut schema: Schema = self.df.schema().to_owned().into();
-        let mut projection: Option<SchemaRef> = Some(Arc::new(schema.clone()));
+        let mut projection: Option<SchemaRef> = None;
 
         if let Some(schema_capsule) = requested_schema {
             validate_pycapsule(&schema_capsule, "arrow_schema")?;