perf: Use Vec::with_capacity in cast_to_run_end_encoded (#8726)

Related to #8707.

Inspired by
#8716 (comment), a
follow up improvement to #8589: We already know what the length of the
two vectors will be, so we can create them with that capacity.

Author: vegarsti

arrow-cast/src/cast/run_array.rs

@@ -136,8 +136,9 @@ pub(crate) fn cast_to_run_end_encoded<K: RunEndIndexType>(
 
     // Partition the array to identify runs of consecutive equal values
     let partitions = partition(&[Arc::clone(cast_array)])?;
-    let mut run_ends = Vec::new();
-    let mut values_indexes = Vec::new();
+    let size = partitions.len();
+    let mut run_ends = Vec::with_capacity(size);
+    let mut values_indexes = Vec::with_capacity(size);
     let mut last_partition_end = 0;
     for partition in partitions.ranges() {
         values_indexes.push(last_partition_end);