Virtual node cache and virtual data source to use hash chunks

[artemananiev]

This is a part of Virtual Map Chunkify effort: #5286 - and a follow-up for #20198.

Past chunkify prototypes showed no improvements (sometimes even regressions), because the node cache still operated with individual hashes rather than chunks. As a result, there were issues with clean caches during flushes, and other problems. The right approach is to switch both VirtualNodeCache and VirtualDataSource to work with chunks.