Fix optimizer factory usage in Sandwiching

[odow]

Closes #146

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.82%. Comparing base (10ab254) to head (def5568).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #148      +/-   ##
==========================================
+ Coverage   99.73%   99.82%   +0.08%     
==========================================
  Files          12       12              
  Lines        1127     1127              
==========================================
+ Hits         1124     1125       +1     
+ Misses          3        2       -1     

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