Flattener: Flatten class template parameters

[ajor]

No description provided.

[codecov-commenter]

Codecov Report

Merging #191 (529e251) into main (ceafce8) will increase coverage by 0.03%.
The diff coverage is 92.85%.

@@            Coverage Diff             @@
##             main     #191      +/-   ##
==========================================
+ Coverage   64.31%   64.34%   +0.03%     
==========================================
  Files          87       87              
  Lines        9429     9441      +12     
  Branches     1553     1555       +2     
==========================================
+ Hits         6064     6075      +11     
  Misses       2542     2542              
- Partials      823      824       +1     

Impacted Files	Coverage Δ
test/test_flattener.cpp	95.03% <90.00%> (-0.18%)	⬇️
oi/type_graph/Flattener.cpp	90.47% <100.00%> (+0.23%)	⬆️

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