[ncp] add ncp_cli_join_leave.exp for CLI testing under NCP mode

[yangsong-cnyn]

This PR introduces a new expect test script, ncp_cli_join_leave.exp, designed to verify the functionality of joining and leaving using the ot-ctl CLI under NCP mode.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.74%. Comparing base (2b41187) to head (6b3b60f).
Report is 1034 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2821       +/-   ##
===========================================
- Coverage   55.77%   43.74%   -12.04%     
===========================================
  Files          87      114       +27     
  Lines        6890    13919     +7029     
  Branches        0      982      +982     
===========================================
+ Hits         3843     6089     +2246     
- Misses       3047     7508     +4461     
- Partials        0      322      +322     

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[Irving-cl]

LGTM 👍

A small issue. Add please update the PR title and description.

[Copilot]

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Files not reviewed (3)

• tests/scripts/expect/_common.exp: Language not supported
• tests/scripts/expect/ncp_cli_join_leave.exp: Language not supported
• tests/scripts/ncp_mode: Language not supported