aiofastnet integration

[tarasko]

What do these changes do?

Use aiofastnet provided function like create_connection and create_server to speed-up networking and allow native sendfile for TLS connections.

Are there changes in behavior for the user?

No

Is it a substantial burden for the maintainers to support this?

Maybe aiofastnet can be added as an extra, users would have to explicitly enable it.
aiofastnet provides drop-in replacements for asyncio networking function so from aiohttp perspective the changes are trivial.

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
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