Chunk function for CSR sparse arrays

[Mystic-Slice]

Figured out how to obtain the data specific to each process. Should be efficient enough.

Question:

What should happen to the Row indices vector?

The row indices keep track of the number of non-zero elements before that row. Since we are splitting it into chunks, the original row index vector (or a part of it) no longer makes sense in the local array. Building a new row index vector also seems pointless because I don't see how that would be useful in matrix operations.

[mtar]

GPU cluster tests are currently disabled on this Pull Request.

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