Support for last_k temporal sampling strategy

[rusty1s]

No description provided.

[codecov-commenter]

Codecov Report

Merging #114 (b160345) into master (9eea511) will decrease coverage by 0.13%.
The diff coverage is 90.90%.

@@            Coverage Diff             @@
##           master     #114      +/-   ##
==========================================
- Coverage   89.32%   89.18%   -0.14%     
==========================================
  Files          16       16              
  Lines         412      416       +4     
==========================================
+ Hits          368      371       +3     
- Misses         44       45       +1     

Impacted Files	Coverage Δ
pyg_lib/csrc/sampler/cpu/neighbor_kernel.cpp	89.18% <85.71%> (-0.54%)	⬇️
pyg_lib/csrc/sampler/neighbor.cpp	100.00% <100.00%> (ø)

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