FIX-#416: Add missing files into sdist #844

Job	Run time
lint (black)	5s
lint (flake8)	9s
test-ubuntu (backend ray, python 3.8)	1m 37s
test-ubuntu (backend mpi, python 3.8)	1m 37s
test-ubuntu (backend dask, python 3.8)	1m 36s
test-ubuntu (backend pymp, python 3.8)	1m 35s
test-ubuntu (backend pyseq, python 3.8)	1m 41s
test-ubuntu (backend ray, python 3.9)	1m 35s
test-ubuntu (backend mpi, python 3.9)	1m 37s
test-ubuntu (backend dask, python 3.9)	1m 37s
test-ubuntu (backend pymp, python 3.9)	1m 30s
test-ubuntu (backend pyseq, python 3.9)	1m 37s
test-windows (backend ray, python 3.8)	1m 43s
test-windows (backend mpi, python 3.8)	1m 40s
test-windows (backend dask, python 3.8)	1m 39s
test-windows (backend pymp, python 3.8)	1m 39s
test-windows (backend pyseq, python 3.8)	1m 44s
test-windows (backend ray, python 3.9)	1m 39s
test-windows (backend mpi, python 3.9)	1m 44s
test-windows (backend dask, python 3.9)	1m 40s
test-windows (backend pymp, python 3.9)	1m 42s
test-windows (backend pyseq, python 3.9)	1m 39s
	33m 5s

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