Summary

I noticed that _CachedRequest at starlette.middleware.base had uncomplete stream() generator caching (_wrapped_rc_stream), so I fixed that

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)

• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.

• I've updated the documentation accordingly.