Global string dedup cache

[Bnaya]

Strings have reference counting, and we save duplicate strings once for every save operation.
It's easy for us, because we create cache at the beginning of the save operation.

But can we do that across different save operations?
If we keep that cache aways alive, it might get stale, leak memory, and won't be useful for other threads.

So the "ultimate" and complex solution would be global string registry inside the objectbuffer memory
(To hold all strings in additional data struct that we can locate them easily)