[issue41305] Add StreamReader.readinto()

[Tony]

Change by Tony <tony.solomonik at gmail.com>:


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keywords: +patch
pull_requests: +20634
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/21491

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41305>
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