Async stream upload

[kylebarron]

Change list

• Add support for sync iterators and async iterators in obstore.put.
  • Improved PutInput concept, which is an enum over pull-based sources, sync push-based sources, and async push-based sources.
  • Previous accepted input into PutInput is now contained in PullSource, including files on disk, file-like objects, and buffers.
  • Now there's both SyncPushSource, which covers sync iterators emitting buffer protocol objects, and AsyncPushSource, which covers async iterators emitting buffer protocol objects.
• Add tests.
• More detailed exceptions by using Debug instead of Display on the rust side.
• Add note in BytesStream docstring about making the timeout parameter longer.
• Rename Buffer to Bytes in type hints (from Use pyo3-bytes from obstore #128)
• Add BytesStream to website docs
• Update documentation

Closes #47

[kylebarron]

It turns out that the error I was previously hitting was just the request timeout, since I was downloading a large file.