Reduced redundant operators

Sometimes at the same time there are operators like A->B, B->C, A->C where one of A->B and B->C should be eliminated otherwise some redundant operators will be created.

For example, we have 3 stores with data size of (100G, 80G, 20G), the `balance-region-scheduler` will create 3 types of operators to transfer region: 100G->20G, 100G->80G, 80G->20G, the second one is redundant.

This can happen across multiple schedulers too.

Start by tracing the balance-region-scheduler and the paths that combine operators from multiple schedulers. Determine where transfer relationships such as A->B, B->C, and A->C are produced, then define tests showing that redundant transfers are not created while necessary operators remain.

Written by the indexing model from the issue text.