adds grpc serving error tests

[mchmarny]

No new logic, only tests

[codecov]

Codecov Report

Merging #102 into main will increase coverage by 7.28%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #102      +/-   ##
==========================================
+ Coverage   69.02%   76.31%   +7.28%     
==========================================
  Files          14       14              
  Lines         494      494              
==========================================
+ Hits          341      377      +36     
+ Misses        101       73      -28     
+ Partials       52       44       -8     

Impacted Files	Coverage Δ
service/grpc/service.go	66.66% <0.00%> (+16.66%)	⬆️
service/grpc/invoke.go	83.87% <0.00%> (+19.35%)	⬆️
service/grpc/binding.go	91.66% <0.00%> (+37.49%)	⬆️
service/grpc/topic.go	87.23% <0.00%> (+38.29%)	⬆️

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