[Feature] Multiple constraints on mutually exclusive sets of items

[akshayka]

It is in principle possible to have multiple constraint sets, so long as the constraints are on mutually exclusive subsets of the items.

For example, for n=1000 items, the vectors of items 0, ..., 99 could be anchored in place, while the submatrix of the embedding for items 100, ..., 999 could constrained to be standardized.