[GraphBolt] extend regression tests for pipelining optimization

[Rhett-Ying]

🔨Work Item

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Project tracker: https://github.com/orgs/dmlc/projects/2

Description

we need to extend the regression tests to cover sample_layer_neigbor and dataloader's overlap_graph_sampling arguments to verify the optimization in #7039.

Depending work items or issues

[Rhett-Ying]

@mfbalin please add more context to help @caojy1998 on this work item.

[mfbalin]

We can modify the https://github.com/dmlc/dgl/blob/master/examples/sampling/graphbolt/node_classification.py to add a sampler option to switch between sample_neighbors and sample_layer_neighbors.

Also, a boolean argument called --overlap_graph_fetch to be passed into the gb.Dataloader, https://docs.dgl.ai/en/latest/generated/dgl.graphbolt.DataLoader.html#dgl.graphbolt.DataLoader.

The regression tests will then need to be updated to cover the combination of the relevant variables, note that overlap_graph_fetch is applicable only for the GPU.

[caojy1998]

Done in PR: https://github.com/dglai/DGL_scripts/pull/186