feat. mapping Optimized error stack

[reatang]

Optimize error returns to allow external parties to better judge errors

I can set an error handler to accurately handle error parameters with a single judgment.

httpx.SetErrorHandler(func(err error) (int, any) {
      if errors.Is(err, mapping.ErrMappingErrors) {
	      return http.StatusBadRequest, nil
      }
      
      return http.StatusInternalServerError, nil
})

[codecov]

Codecov Report

Attention: Patch coverage is 85.52632% with 11 lines in your changes missing coverage. Please review.

Project coverage is 95.10%. Comparing base (8690859) to head (bb60a0a).
Report is 58 commits behind head on master.

Additional details and impacted files

Files	Coverage Δ
core/mapping/fieldoptions.go	100.00% <100.00%> (ø)
core/mapping/marshaler.go	100.00% <100.00%> (ø)
core/mapping/utils.go	100.00% <100.00%> (ø)
core/mapping/unmarshaler.go	96.33% <73.17%> (-0.15%)	⬇️

... and 251 files with indirect coverage changes