edges iterates over Graphs.Edge

[CarloLucibello]

returning Graphs.Edge types instead of tuples allows better interaction with the graph ecosystem.
For example, now we can plot a graph with

using GraphNeuralNetworks, GraphMakie, GLMakie

g = rand_graph(10, 30)

graphplot(g)

[codecov]

Codecov Report

Merging #171 (939dbfc) into master (71f0355) will increase coverage by 0.08%.
The diff coverage is 100.00%.

❗ Current head 939dbfc differs from pull request most recent head c154465. Consider uploading reports for the commit c154465 to get more accurate results

@@            Coverage Diff             @@
##           master     #171      +/-   ##
==========================================
+ Coverage   85.38%   85.47%   +0.08%     
==========================================
  Files          15       15              
  Lines        1300     1301       +1     
==========================================
+ Hits         1110     1112       +2     
+ Misses        190      189       -1     

Impacted Files	Coverage Δ
src/msgpass.jl	73.80% <ø> (ø)
src/GNNGraphs/gnngraph.jl	75.00% <100.00%> (+0.33%)	⬆️
src/GNNGraphs/query.jl	93.56% <100.00%> (+0.58%)	⬆️

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