Incorrect accounting in `DictEncoder::estimated_memory_size`

[mzabaluev]

In parquet, the estimated_memory_size method of DictEncoder should estimate the actual usage of allocated memory, but instead it uses the data member counting the encoded size of dictionary data, and ignores the hash table memory usage added by the Interner member.

[mzabaluev]

Code reference:

arrow-rs/parquet/src/encodings/encoding/dict_encoder.rs

Line 185 in 88b7fca

fn estimated_memory_size(&self) -> usize {