Optimize cursor creation

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At each cursor generation step, a new cursor and a large number of subcursors are created as intermediate stages of generation using suboptimal logic, while access to subcursors is isolated, and using intermediate cursors of one generation for another is bad practice.

Head-on solution: implement creation of new cursors only at a start of generation using a flag attribute and rewrite functions for creating intermediate generation cursors and subcursors from immutable to mutable with a return of not a new one but a modified current one.