refactor(poly): work with indexes

[cyphersnake]

At the moment, information about how we define the layout of Expression::Polynomial index handling is scattered throughout the codebase and there is a high chance of error and there is a high chance of error. Within #233, the QueryIndexContext type was introduced which solves this problem, but only partially.

It is necessary to either redo the work with indexes (make them relative) and bring information about the subtype into Expression::Polynomial, or localize the work with absolute indexes within QueryIndexContext throughout the code base