Improve writing into HTTP/2 streams without a read-able object

[easysong]

As soon as I call start_stream_transcription, this module use cpu 100%.
The reason is that BufferableByteStream's read function keeps calling without sleep,
but I don't know where it is called.

[joguSD]

@easysong Yes, this is a known issue right now. The reason you can't find where it's called is because it happens on the C side of the aws crt Python bindings. The aws crt doesn't currently provide an interface for writing into an HTTP/2 stream on the Python side of things. The best we can do right now is provide a file-like object with a read that has some quirky behavior, like the one you're mentioning.