perf: Batch nested embed parquet decoding

This continues on #17542 and now also batches the actual Nesting, not only the top decoder.

I did the same benchmark with `POLARS_MAX_THREADS=1` and we again see a small
speedup. But I suspect that the speedup is larger for `FixedSizeList`s and
`Struct`s.

```
Benchmark 1: After Optimization
  Time (mean ± σ):     13.306 s ±  0.018 s    [User: 12.661 s, System: 0.614 s]
  Range (min … max):   13.263 s … 13.335 s    10 runs

Benchmark 2: Before Optimization
  Time (mean ± σ):     14.973 s ±  0.065 s    [User: 14.422 s, System: 0.517 s]
  Range (min … max):   14.887 s … 15.129 s    10 runs

Summary
  After Optimization ran
    1.13 ± 0.01 times faster than Before Optimization
```

crates/polars-parquet/src/arrow/read/deserialize/binary/utils.rs

@@ -108,7 +108,8 @@ impl<'a> Iterator for BinaryIter<'a> {
 
     #[inline]
     fn next(&mut self) -> Option<Self::Item> {
-        if self.values.is_empty() || self.num_values == 0 {
+        if self.num_values == 0 {
+            assert!(self.values.is_empty());
             return None;
         }
 

crates/polars-parquet/src/arrow/read/deserialize/mod.rs

@@ -46,7 +46,7 @@ pub fn create_list(
     nested: &mut NestedState,
     values: Box<dyn Array>,
 ) -> Box<dyn Array> {
-    let (mut offsets, validity) = nested.nested.pop().unwrap().take();
+    let (mut offsets, validity) = nested.pop().unwrap();
     match data_type.to_logical_type() {
         ArrowDataType::List(_) => {
             offsets.push(values.len() as i64);
@@ -89,7 +89,7 @@ pub fn create_map(
     nested: &mut NestedState,
     values: Box<dyn Array>,
 ) -> Box<dyn Array> {
-    let (mut offsets, validity) = nested.nested.pop().unwrap().take();
+    let (mut offsets, validity) = nested.pop().unwrap();
     match data_type.to_logical_type() {
         ArrowDataType::Map(_, _) => {
             offsets.push(values.len() as i64);
@@ -147,7 +147,7 @@ where
                 chunk_size,
                 num_rows,
             )?
-            .map(|x| Ok((NestedState::new(vec![]), x?))),
+            .map(|x| Ok((NestedState::default(), x?))),
         ));
     }
 

crates/polars-parquet/src/arrow/read/deserialize/nested.rs

@@ -13,7 +13,7 @@ where
 {
     Box::new(iter.map(|x| {
         x.map(|(mut nested, array)| {
-            let _ = nested.nested.pop().unwrap(); // the primitive
+            let _ = nested.pop().unwrap(); // the primitive
             (nested, array)
         })
     }))
@@ -28,7 +28,7 @@ where
 {
     Box::new(iter.map(|x| {
         x.map(|(mut nested, array)| {
-            let _ = nested.nested.pop().unwrap(); // the primitive
+            let _ = nested.pop().unwrap(); // the primitive
             (nested, Box::new(array) as _)
         })
     }))
@@ -322,7 +322,7 @@ where
                                 validity,
                             )?);
 
-                            let _ = nested.nested.pop().unwrap(); // the primitive
+                            let _ = nested.pop().unwrap(); // the primitive
 
                             Ok((nested, array))
                         });
@@ -380,7 +380,7 @@ where
                                 validity,
                             )?);
 
-                            let _ = nested.nested.pop().unwrap(); // the primitive
+                            let _ = nested.pop().unwrap(); // the primitive
 
                             Ok((nested, array))
                         });
@@ -411,7 +411,7 @@ where
                                 validity,
                             )?);
 
-                            let _ = nested.nested.pop().unwrap(); // the primitive
+                            let _ = nested.pop().unwrap(); // the primitive
 
                             Ok((nested, array))
                         });