fix: correct DictEncoder::estimated_memory_size

The returned value should estimate the actual memory usage, but
instead it used the evaluation of the encoded size of the dictionary
data, and bypassed the hash table memory usage added by the Interner.
The implementation of Storage::estimated_memory_size for the
unique key storage was not correct as well, but it was unused.
Correct both problems.

Author: mzabaluev

parquet/src/encodings/encoding/dict_encoder.rs

@@ -64,7 +64,7 @@ impl<T: DataType> Storage for KeyStorage<T> {
     }
 
     fn estimated_memory_size(&self) -> usize {
-        self.size_in_bytes + self.uniques.capacity() * std::mem::size_of::<T::T>()
+        self.uniques.capacity() * std::mem::size_of::<T::T>()
     }
 }
 
@@ -183,6 +183,6 @@ impl<T: DataType> Encoder<T> for DictEncoder<T> {
     ///
     /// For this encoder, the indices are unencoded bytes (refer to [`Self::write_indices`]).
     fn estimated_memory_size(&self) -> usize {
-        self.interner.storage().size_in_bytes + self.indices.len() * std::mem::size_of::<usize>()
+        self.interner.estimated_memory_size() + self.indices.len() * std::mem::size_of::<usize>()
     }
 }