add benchmarks (PkgBenchmark)

[CarloLucibello]

No description provided.

[codecov]

Codecov Report

Merging #137 (660dfcf) into master (77f0e0f) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #137   +/-   ##
=======================================
  Coverage   85.36%   85.36%           
=======================================
  Files          15       15           
  Lines        1257     1237   -20     
=======================================
- Hits         1073     1056   -17     
+ Misses        184      181    -3     

Impacted Files	Coverage Δ
src/GNNGraphs/utils.jl	73.19% <0.00%> (-2.06%)	⬇️
src/GNNGraphs/convert.jl	89.91% <0.00%> (-0.49%)	⬇️
src/GNNGraphs/query.jl	92.94% <0.00%> (-0.09%)	⬇️
src/GNNGraphs/transform.jl	96.71% <0.00%> (-0.04%)	⬇️
src/GNNGraphs/sampling.jl	100.00% <0.00%> (ø)
src/layers/conv.jl	79.52% <0.00%> (+0.17%)	⬆️
src/GNNGraphs/gnngraph.jl	77.61% <0.00%> (+3.32%)	⬆️

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