ExaTN-Gen visitor: support reconstruction period specified by both gate and layer count

[1tnguyen]

The exaTN-Gen visitor to support two modes:

• option for a reconstruct_gates: current behavior

• option reconstruct_layers: counting layers (gates acting on disjoint subsets of qubits).

Currently, the visitor only supports reconstruction by 2-body gate counting.

[DmitryLyakh]

Also, the reconstruction activation condition should become always true when reaching the last layer/gate.