FEAT-#285: Implement shared object storage for MPI backend #649

Job	Run time
lint (black)	11s
lint (flake8)	10s
test-ubuntu (backend ray, python 3.8)	7m 36s
test-ubuntu (backend mpi, python 3.8)	7m 47s
test-ubuntu (backend dask, python 3.8)	7m 5s
test-ubuntu (backend pymp, python 3.8)	6m 31s
test-ubuntu (backend pyseq, python 3.8)	6m 42s
test-ubuntu (backend ray, python 3.9)	41s
test-ubuntu (backend mpi, python 3.9)	5m 29s
test-ubuntu (backend dask, python 3.9)	6m 31s
test-ubuntu (backend pymp, python 3.9)	2m 28s
test-ubuntu (backend pyseq, python 3.9)	1m 2s
test-windows (backend ray, python 3.8)	1s
test-windows (backend mpi, python 3.8)	1s
test-windows (backend dask, python 3.8)	12s
test-windows (backend pymp, python 3.8)	1s
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)	1s
test-windows (backend pymp, python 3.9)	1s
test-windows (backend pyseq, python 3.9)	1s
	52m 34s

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