move "batch size estimation" biz-logic from SD to Exec

[AskAlexSharov]

reason:

• it creating chicken-egg problem. Can't print in logs size before commitment, then print after commitment - and understand how much data produced commitment. Because "print after" will show over-estimated size.
• SD is now having less and less biz-logic. So, EstimateSize it's clearly abstraction-leak

Before this change i see:

buf=512M before commitment
buf=9G after commitment

but it's not because Commitment producing so much data
it's because we "double-estimate": using estimation logic which "predicting RAM usage after Commitment - before commitment", use same prediction "after Commitment" is incorrect - because "we just know how much RAM we using now".