Make ArrowArrayStreamReader Send

[wjones127]

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

ArrowArrayStreamReader is not Send, which makes is very difficult to work with in async contexts.

While FFI_ArrowArrayStream shouldn't be Sync, I do think it should be marked Send. From the docs:

The stream source is not assumed to be thread-safe. Consumers wanting to call get_next from several threads should ensure those calls are serialized.

Describe the solution you'd like

If FFI_ArrowArrayStream were marked Send and ArrowArrayStreamReader were refactored to hold the inner type in a Box rather than an Arc, then it would be Send.

Describe alternatives you've considered

Additional context

[tustvold]

label_issue.py automatically added labels {'arrow'} from #4232