Lift an UStore to another UStore which contains all the entries of the former under given field.

This function is not intended for use in migrations, only in normal entry points.

Note that this function ensures that template of resulting store does not contain inner nested templates with duplicated fields, otherwise UStore invariants could get broken.

Unlift an UStore to a smaller UStore which is part of the former.

This function is not intended for use in migrations, only in normal entry points.

Surprisingly, despite smaller UStore may have extra entries, this function is safe when used in contract code. Truly, all getters and setters are still safe to use. Also, there is no way for the resulting small UStore to leak outside of the contract since the only place where big_map can appear is contract storage, so this small UStore can be either dropped or lifted back via liftUStore to appear as part of the new contract's state.

When this function is run as part of standalone instructions sequence, not as part of contract code (e.g. in tests), you may get an UStore with entries not inherent to it.