FEAT-#285: Implement shared object storage for MPI backend #658

Job	Run time
lint (flake8)	9s
lint (black)	7s
test-ubuntu (backend ray, python 3.8)	6m 37s
test-ubuntu (backend mpi, python 3.8)	6m 35s
test-ubuntu (backend dask, python 3.8)	6m 38s
test-ubuntu (backend pymp, python 3.8)	6m 40s
test-ubuntu (backend pyseq, python 3.8)	6m 39s
test-ubuntu (backend ray, python 3.9)	6m 38s
test-ubuntu (backend mpi, python 3.9)	6m 37s
test-ubuntu (backend dask, python 3.9)	6m 39s
test-ubuntu (backend pymp, python 3.9)	6m 13s
test-ubuntu (backend pyseq, python 3.9)	6m 35s
test-windows (backend ray, python 3.8)	6m 36s
test-windows (backend mpi, python 3.8)	6m 38s
test-windows (backend dask, python 3.8)	6m 38s
test-windows (backend pymp, python 3.8)	6m 37s
test-windows (backend pyseq, python 3.8)	1s
test-windows (backend ray, python 3.9)	1s
test-windows (backend mpi, python 3.9)	1s
test-windows (backend dask, python 3.9)	15s
test-windows (backend pymp, python 3.9)	1s
test-windows (backend pyseq, python 3.9)	1s
	1h 32m 56s

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