Di graph support

[rjcortese]

Hello,
This is for #203.
It picks up where #200 left off.
I think I've made necessary changes except for some finishing the tests... but I could use a review and feedback :)

[arcondello]

Thanks for the PR! A few minor things but overall seems to be going in the right direction

[codecov-commenter]

Codecov Report

Merging #205 (96cb92b) into main (cbf0ea5) will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #205      +/-   ##
==========================================
+ Coverage   71.15%   71.32%   +0.16%     
==========================================
  Files          29       29              
  Lines        1751     1761      +10     
==========================================
+ Hits         1246     1256      +10     
  Misses        505      505              

Impacted Files	Coverage Δ
dwave_networkx/algorithms/tsp.py	100.00% <100.00%> (ø)

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[arcondello]

Looks good to me. This is ready to merge?

[rjcortese]

Only thing left I guess is some test related stuff... I'm not sure how to test QUBO returned from dnx.traveling_salesperson_qubo(G, missing_edge_weight=1). I made a comment regarding it in the code.
Thoughts?

[rjcortese]

This is ready to merge now imo :)