refactor(gen): return ErrNotImplemented, if nameGen unable to generate name

[tdakkota]

No description provided.

[codecov]

Codecov Report

Merging #190 (9340c09) into main (f917bb9) will decrease coverage by 1.30%.
The diff coverage is 37.89%.

@@            Coverage Diff             @@
##             main     #190      +/-   ##
==========================================
- Coverage   68.01%   66.71%   -1.31%     
==========================================
  Files          99      100       +1     
  Lines        6275     6417     +142     
==========================================
+ Hits         4268     4281      +13     
- Misses       1759     1860     +101     
- Partials      248      276      +28     

Impacted Files	Coverage Δ
gen/gen_request_body.go	41.46% <0.00%> (-10.06%)	⬇️
gen/generator.go	51.51% <0.00%> (-7.22%)	⬇️
gen/templates.go	89.92% <ø> (ø)
gen/fix.go	50.26% <27.02%> (-6.18%)	⬇️
gen/gen_parameters.go	52.45% <30.00%> (-4.56%)	⬇️
gen/generics.go	48.35% <31.25%> (-4.82%)	⬇️
gen/schema_gen_primitive.go	87.50% <35.71%> (-9.10%)	⬇️
gen/gen_contents.go	83.01% <40.00%> (-5.22%)	⬇️
gen/gen_responses.go	66.34% <41.93%> (-6.10%)	⬇️
gen/walk.go	52.63% <43.75%> (-47.37%)	⬇️
... and 13 more

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