[posix] Add POSIX Cli Daemon module

[yangsong-cnyn]

This PR introduces the CLI daemon module for OTBR on POSIX in NCP mode. This initial implementation focuses on setting up the module and establishing the listen socket. Further CLI functionalities and integration with NcpHost will be implemented in subsequent PRs.

[codecov]

Codecov Report

Attention: Patch coverage is 72.72727% with 12 lines in your changes missing coverage. Please review.

Project coverage is 43.41%. Comparing base (2b41187) to head (b5e7645).
Report is 952 commits behind head on main.

Files with missing lines	Patch %	Lines
src/host/posix/cli_daemon.cpp	72.41%	8 Missing ⚠️
tests/gtest/test_cli_daemon.cpp	73.33%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2676       +/-   ##
===========================================
- Coverage   55.77%   43.41%   -12.37%     
===========================================
  Files          87      110       +23     
  Lines        6890    13448     +6558     
  Branches        0      963      +963     
===========================================
+ Hits         3843     5838     +1995     
- Misses       3047     7303     +4256     
- Partials        0      307      +307     

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[Irving-cl]

Thanks for the quick implementation 👍

I have a few comments.

[Irving-cl]

I think the CLI module on NCP should initialize at first and the initialization isn't triggered by and message from the host. Thoughts?

[Irving-cl]

Please abstract this process as an interface and this interface can be implememted by NcpSpinel (or some classes under RCP mode in the future). In this way, we can use this module for both NCP and RCP (later we transition to use this module). In addition, we can have a test implementation of this interface and write unit tests.

You may refer to Netif::Dependencies and tests/gtest/test_netif.cpp. The scheme will be very similar.

Then please add a unit test similar as test_netif.cpp. In the test, we simply create an instance of the Daemon class and a Mainloop. And we can also create a client socket and write cli commands to the socket. Then run the mainloop. Next we can check the call of our test implementation of the interface.

To run the gtest, build otbr-agent with -DBUILD_TESTING=ON flag. (By default it should be turned on)
Then run ${YOUR_BUILD_DIR}/tests/gtest/${YOUR_GTEST_PROGRAM}.

[Irving-cl]

LGTM 👍

Thanks for breaking it into small ones.

[superwhd]

LGTM overall