WIP: test that webgraph supports duplicate edges

swh/graph/tests/dataset/example.edges.csv

swh/graph/tests/dataset/example.edges.csv.zst

swh/graph/tests/dataset/img/example.dot

swh/graph/tests/dataset/output/example-transposed.graph

swh/graph/tests/dataset/output/example-transposed.obl

swh/graph/tests/dataset/output/example-transposed.offsets

swh/graph/tests/dataset/output/example-transposed.properties

swh/graph/tests/dataset/output/example.graph

swh/graph/tests/dataset/output/example.mph

swh/graph/tests/dataset/output/example.node2pid.bin

swh/graph/tests/dataset/output/example.node2type.map

swh/graph/tests/dataset/output/example.obl

swh/graph/tests/dataset/output/example.offsets

swh/graph/tests/dataset/output/example.order

swh/graph/tests/dataset/output/example.pid2node.bin

swh/graph/tests/dataset/output/example.properties

swh/graph/tests/dataset/output/example.stats

swh/graph/tests/test_graph.py