Function should_merge_dictionary_values 

pub(crate) fn should_merge_dictionary_values<K: ArrowDictionaryKeyType>(
    dictionaries: &[&DictionaryArray<K>],
    len: usize,
) -> (bool, bool)

A weak heuristic of whether to merge dictionary values that aims to only perform the expensive merge computation when it is likely to yield at least some return over the naive approach used by MutableArrayData

len is the total length of the merged output

Returns (should_merge, has_overflow) where:

• should_merge: whether dictionary values should be merged
• has_overflow: whether the combined dictionary values would overflow the key type