Constructs an Appender with a given array. Note that this does not copy the
data. If the array has a larger capacity as determined by arr.capacity,
it will be used by the appender. After initializing an appender on an array,
appending to the original array will reallocate.
Constructs an Appender with a given array. Note that this does not copy the data. If the array has a larger capacity as determined by arr.capacity, it will be used by the appender. After initializing an appender on an array, appending to the original array will reallocate.