[REVIEW]Fix Fanout -1

[VibhuJawa]

This PR fixes sampling when for the default value of -1 which is called below:

cugraph/python/cugraph/cugraph/gnn/graph_store.py

Lines 129 to 133 in 92f6ba4

	filtered_list = sample_groups(filtered_list,
	by="dst",
	n_samples=fanout)
	return filtered_list['dst'].values, filtered_list['src'].values

In workflows this is called during inference so we need this to work for inference to work .with CuGraphStorage .

[rlratzel]

The code change and test LGTM and I'll just approve now, but I have one small request: could you also update the docstring here to indicate that -1 now returns all samples?

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (branch-22.08@c837aaa). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff               @@
##             branch-22.08    #2358   +/-   ##
===============================================
  Coverage                ?   60.76%           
===============================================
  Files                   ?      105           
  Lines                   ?     5077           
  Branches                ?        0           
===============================================
  Hits                    ?     3085           
  Misses                  ?     1992           
  Partials                ?        0           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c837aaa...7fda2b2. Read the comment docs.

[VibhuJawa]

The code change and test LGTM and I'll just approve now, but I have one small request: could you also update the docstring here to indicate that -1 now returns all samples?

Added that. Also for full visibility this makes it align with the DGL behavior mentioned here.

https://github.com/dmlc/dgl/blob/b258729b3f0613ef685d40b1ad51a84f455745c5/python/dgl/sampling/neighbor.py#L182-L183

[rlratzel]

@gpucibot merge