Specified version of helper function to cast binary to string

[viirya]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Describe the solution you'd like

We can avoid re-encoding the offsets when not necessary in the helper function to cast from binary to string.

Describe alternatives you've considered

Additional context

[tustvold]

label_issue.py automatically added labels {'arrow'} from #3624