[GraphBolt] Refactor sampling

[RamonZhou]

Description

Refactor NeighborSampling and TemporalNeighborSampling.

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• I've leverage the tools to beautify the python and c++ code.
• The PR is complete and small, read the Google eng practice (CL equals to PR) to understand more about small PR. In DGL, we consider PRs with less than 200 lines of core code change are small (example, test and documentation could be exempted).
• All changes have test coverage
• Code is well-documented
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
• Related issue is referred in this PR
• If the PR is for a new model/paper, I've updated the example index here.

Changes

[dgl-bot]

To trigger regression tests:

• @dgl-bot run [instance-type] [which tests] [compare-with-branch];
  For example: @dgl-bot run g4dn.4xlarge all dmlc/master or @dgl-bot run c5.9xlarge kernel,api dmlc/master

[dgl-bot]

Commit ID: d16ed9c

Build ID: 1

Status: ✅ CI test succeeded.

Report path: link

Full logs path: link

[mfbalin]

How did the MSVC bug get resolved?

[mfbalin]

Depends on #7369.

[mfbalin]

@RamonZhou can you merge latest changes by updating branch and test the hetero example?

[dgl-bot]

Commit ID: 8a880c2

Build ID: 2

Status: ✅ CI test succeeded.

Report path: link

Full logs path: link

[RamonZhou]

@RamonZhou can you merge latest changes by updating branch and test the hetero example?

@mfbalin I tested hetero_rgcn (CPU) on my local machine and it goes from 248.9s to 235.1s (per epoch), 5.5% improvement.

[mfbalin]

@RamonZhou can you merge latest changes by updating branch and test the hetero example?

@mfbalin I tested hetero_rgcn (CPU) on my local machine and it goes from 248.9s to 235.1s (per epoch), 5.5% improvement.

That is because no GPU is there for forward backward. More improvement is expected when forward backward runs on the GPU. Cool, good work overall!