Fix empty unnamed struct matcher generation

[p-jahn]

Fixes #101

• by replacing the name of unnamed struct{} types
• restrictive naming because non-empty struct{} types cannot be handled (yet) and are excluded here

  pegomock/modelgen/gomock/parse.go

  Line 358 in 5482ace

  return nil, p.errorf(v.Pos(), "can't handle non-empty unnamed struct types")

[petergtz]

Super cool! Nothing to add :-). Thanks very much, @p-jahn . Merging!

[jpopadak]

🙇🏼 Thank you! :) Allows me to get rid of: rm internal/service/matchers/recv_chan_of_struct{}.go