Chunking apply_fun for MCState.to_array

Created by: alleSini99

MCState.to_array() cannot be used to instantiate the wave function over the full Hilbert space for systems with fairly large size (but that should be still accessible) due to a large memory usage. The modification in MCState.to_array() consists in the possibility of computing the wave function over chunks of the Hilbert space of size MCState.chunk_size that are then combined to get the complete state vector.