Extract file receiver from BackupManager.async_receive_backup to util

[emontnemery]

Proposed change

Extract file receiver from BackupManager.async_receive_backup to improve core readability and allowing it to be reused

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• Dependency upgrade
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[home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (backup) you are listed as a code owner for? Thanks!

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[MartinHjelmare]

Side note: Why is it important to wait until the chunk is written to disk? Is it to not consume the stream in vain and waste resources?

[emontnemery]

I agree this is strange. It seems like a more obvious solution would be a sempahore initiated at 5 to ensure we don't fill the RAM if http reading is faster than file writing.

We can consider changing this in a follow-up, we should do some performance testing probably.