Fix passing kwargs to dual_optimizer and DualOptimizer

[odow]

Closes #219

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.47%. Comparing base (68d8372) to head (aa72ee9).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #220      +/-   ##
==========================================
+ Coverage   94.20%   94.47%   +0.26%     
==========================================
  Files          14       14              
  Lines         742      742              
==========================================
+ Hits          699      701       +2     
+ Misses         43       41       -2     

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