adds QUIC endpoint specific for turbine connections

[behzadnouri]

Problem

Currently Turbine QUIC is tied to TPU implementation which makes it difficult to make changes without impacting TPU or optimize the code specifically for Turbine.

Summary of Changes

Working towards separating out Turbine QUIC from TPU, the commit adds a new QUIC endpoint implementation specific for turbine connections.
Compared to QUIC code for TPU, in this code:

• Same endpoint sends and receives packets from the same UdpSocket.
• Packets are sent as datagram instead of streams.
• Connection cache can use a different eviction policy from the TPU one.

This commit only adds the new endpoint constructs; following commits will:

• plumb through the endpoint channels to turbine code.
• implement some cache eviction policy.
• add metrics.

[codecov]

Codecov Report

Merging #32294 (ba4d162) into master (77d4632) will decrease coverage by 0.1%.
The diff coverage is 87.9%.

❗ Current head ba4d162 differs from pull request most recent head 2964e14. Consider uploading reports for the commit 2964e14 to get more accurate results

@@            Coverage Diff            @@
##           master   #32294     +/-   ##
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- Coverage    82.1%    82.0%   -0.1%     
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  Files         773      773             
  Lines      209793   209814     +21     
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- Hits       172253   172242     -11     
- Misses      37540    37572     +32     

[joncinque]

Looks really good! I found the whole thing really easy to read, so thanks for keeping it simple. Most of my points are small questions

[joncinque]

Why is this guard needed? Looking quickly into the code, I don't see that Endpoint needs to be in a runtime context.

[behzadnouri]

Without the guard, this surprisingly panics when it executes <quinn::runtime::tokio::TokioRuntime as quinn::runtime::Runtime>::wrap_udp_socket.

[joncinque]

Yikes, that really stinks. Could you add a comment explaining that? It isn't immediately clear from the code

[behzadnouri]

done

[joncinque]

Everything looks good, just the one nit to add a comment about the runtime guard. After that, this can go in

[behzadnouri]

Everything looks good, just the one nit to add a comment about the runtime guard. After that, this can go in

done.