Avoid overallocating arrays in coalesce primitives / views (#9132)

# Which issue does this PR close?

- Closes #9135 

# Rationale for this change
The code was calling `.reserve(batch_size)` which reserves space to at
least `batch_size` additional elements
(https://doc.rust-lang.org/std/vec/struct.Vec.html#method.reserve).

This also improves performance a bit:

```
filter: primitive, 8192, nulls: 0, selectivity: 0.001
                        time:   [59.509 ms 59.660 ms 59.856 ms]
                        change: [−3.0781% −2.7917% −2.4795%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high severe

filter: primitive, 8192, nulls: 0, selectivity: 0.01
                        time:   [6.0072 ms 6.0226 ms 6.0428 ms]
                        change: [−8.7042% −7.1161% −6.0455%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  2 (2.00%) high mild
  2 (2.00%) high severe

Benchmarking filter: primitive, 8192, nulls: 0, selectivity: 0.1: Warming up for 3.0000 s
Warning: Unable to complete 100 samples in 5.0s. You may wish to increase target time to 9.5s, enable flat sampling, or reduce sample count to 50.
filter: primitive, 8192, nulls: 0, selectivity: 0.1
                        time:   [1.8664 ms 1.8709 ms 1.8772 ms]
                        change: [−15.187% −14.905% −14.632%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 11 outliers among 100 measurements (11.00%)
  5 (5.00%) high mild
  6 (6.00%) high severe

filter: primitive, 8192, nulls: 0, selectivity: 0.8
                        time:   [2.5191 ms 2.5444 ms 2.5717 ms]
                        change: [−13.064% −11.414% −10.003%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 2 outliers among 100 measurements (2.00%)
  1 (1.00%) low mild
  1 (1.00%) high severe

Benchmarking filter: primitive, 8192, nulls: 0.1, selectivity: 0.001: Warming up for 3.0000 s
Warning: Unable to complete 100 samples in 5.0s. You may wish to increase target time to 7.7s, or reduce sample count to 60.
filter: primitive, 8192, nulls: 0.1, selectivity: 0.001
                        time:   [76.422 ms 76.671 ms 76.973 ms]
                        change: [−5.5096% −4.0229% −2.8048%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 2 outliers among 100 measurements (2.00%)
  1 (1.00%) high mild
  1 (1.00%) high severe

filter: primitive, 8192, nulls: 0.1, selectivity: 0.01
                        time:   [10.197 ms 10.228 ms 10.262 ms]
                        change: [−3.6627% −3.0569% −2.4919%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high mild

filter: primitive, 8192, nulls: 0.1, selectivity: 0.1
                        time:   [4.6635 ms 4.6750 ms 4.6915 ms]
                        change: [−9.4939% −8.5908% −7.8383%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 7 outliers among 100 measurements (7.00%)
  5 (5.00%) high mild
  2 (2.00%) high severe

filter: primitive, 8192, nulls: 0.1, selectivity: 0.8
                        time:   [4.7777 ms 4.8115 ms 4.8467 ms]
                        change: [−9.9226% −9.1384% −8.3813%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high mild
```

# What changes are included in this PR?
Changes it to use `self.views.reserve(self.batch_size -
self.views.len())` to avoid allocating more than necessary (i.e. 2x the
amount).

# Are these changes tested?

Existing tests

# Are there any user-facing changes?

Author: Dandandan

arrow-select/src/coalesce.rs

@@ -615,6 +615,7 @@ mod tests {
     use crate::concat::concat_batches;
     use arrow_array::builder::StringViewBuilder;
     use arrow_array::cast::AsArray;
+    use arrow_array::types::Int32Type;
     use arrow_array::{
         BinaryViewArray, Int32Array, Int64Array, RecordBatchOptions, StringArray, StringViewArray,
         TimestampNanosecondArray, UInt32Array, UInt64Array,
@@ -1625,6 +1626,11 @@ mod tests {
         // Now should have a completed batch (100 rows total)
         assert!(coalescer.has_completed_batch());
         let output_batch = coalescer.next_completed_batch().unwrap();
+        let size = output_batch
+            .column(0)
+            .as_primitive::<Int32Type>()
+            .get_buffer_memory_size();
+        assert_eq!(size, 400); // 100 rows * 4 bytes each
         assert_eq!(output_batch.num_rows(), 100);
 
         assert_eq!(coalescer.get_buffered_rows(), 0);

arrow-select/src/coalesce/byte_view.rs

@@ -98,7 +98,10 @@ impl<B: ByteViewType> InProgressByteViewArray<B> {
     /// This is done on write (when we know it is necessary) rather than
     /// eagerly to avoid allocations that are not used.
     fn ensure_capacity(&mut self) {
-        self.views.reserve(self.batch_size);
+        if self.views.capacity() == 0 {
+            self.views.reserve(self.batch_size);
+        }
+        debug_assert_eq!(self.views.capacity(), self.batch_size);
     }
 
     /// Finishes in progress buffer, if any

arrow-select/src/coalesce/primitive.rs

@@ -55,7 +55,10 @@ impl<T: ArrowPrimitiveType> InProgressPrimitiveArray<T> {
     /// This is done on write (when we know it is necessary) rather than
     /// eagerly to avoid allocations that are not used.
     fn ensure_capacity(&mut self) {
-        self.current.reserve(self.batch_size);
+        if self.current.capacity() == 0 {
+            self.current.reserve(self.batch_size);
+        }
+        debug_assert_eq!(self.current.capacity(), self.batch_size);
     }
 }