Python: Add tests and fix the issues with `Timestamp` and `ByteStream` (#2431)

* Add `timestamp` type test and fix the conversion error

* Add some tests for `ByteStream` and fix async issues

* Use `__anext__` method instead of `anext`

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Co-authored-by: Matteo Bigoi <1781140+crisidev@users.noreply.github.com>