Add disjoint neighbor sampling test

[rusty1s]

No description provided.

[codecov-commenter]

Codecov Report

Merging #89 (6d7591b) into master (4d4a26b) will increase coverage by 3.53%.
The diff coverage is 100.00%.

❗ Current head 6d7591b differs from pull request most recent head e37059c. Consider uploading reports for the commit e37059c to get more accurate results

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
+ Coverage   74.74%   78.28%   +3.53%     
==========================================
  Files          14       14              
  Lines         392      396       +4     
==========================================
+ Hits          293      310      +17     
+ Misses         99       86      -13     

Impacted Files	Coverage Δ
pyg_lib/csrc/sampler/cpu/neighbor_kernel.cpp	48.30% <ø> (+4.23%)	⬆️
pyg_lib/csrc/utils/cpu/convert.h	100.00% <100.00%> (+55.55%)	⬆️
pyg_lib/csrc/sampler/cpu/mapper.h	91.42% <0.00%> (+8.57%)	⬆️

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