add tcp protocol

[marverlous811]

What

This PR adds TCP protocol for the MIO backend

Change

The significant change is file src/backend/mio.rs, which adds logic for TCP protocol.

• I created TcpListenerContainer to keep the TCP listener. If one connection is connected to the TCP listener, it will save TcpStreamContainer inside it.
• Because each connection needs to register with the poll as a unique event source, I added an addr_seed_to_token function to create its unique token. That function will generate a token by using the listener port and its connection seed (incrementally when the listener has a new connection).

How to test

• exec RUST_MIN_STACK=6400000 RUST_LOG=info cargo run --example tcp_echo_server command to start the TCP server.
• using the telnet command to connect to that TCP server as a client.

QA

• Why will the event_buffer pop in the next tick instead of instantly after it is processed?

[codecov]

Codecov Report

❌ Patch coverage is 69.82759% with 70 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@10f6b9e). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/backend/mio.rs	76.41%	50 Missing ⚠️
src/task.rs	0.00%	20 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #27   +/-   ##
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  Coverage        ?   52.40%           
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  Files           ?       13           
  Lines           ?     1374           
  Branches        ?        0           
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  Hits            ?      720           
  Misses          ?      654           
  Partials        ?        0           

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