[Optimization] Allow for subtypes of int for edge indexes

[GuillaumeBroggi]

graphorge/src/graphorge/gnn_base_model/data/graph_data.py

Lines 932 to 934 in 31300f5

	elif edges_indexes.dtype != int:
	raise RuntimeError('Edges indexes matrix is not a numpy.array '
	'of dtype int.')

Current behavior enforces int type for edge indexes. Many graphs do not require storing so many indexes; using smaller footprint types can significantly decrease memory usage. For instance, we save 10 GB over ~60k graphs in the cylinder flow dataset when using in16.