v.25.12Improvement

Add support of sparse serialization for columns

Added support of sparse serialization for columns of Nullable type. This continues #44539. #88999 (Amos Bird).
Added support for sparse serialization of columns with Nullable type in ClickHouse.

Why it matters

This feature improves the efficiency of storing and transmitting Nullable columns by enabling sparse serialization, reducing storage space and potentially improving performance when working with tables containing many null values. It continues the enhancement started in issue #44539.

How to use it

This feature is applied automatically when serializing Nullable columns using supported formats that benefit from sparse serialization. No additional user configuration is required.