test: add unit tests for terway package

[l1b0k]

• Add unit tests for tree implementation in terway-cli
• Add unit tests for k8s package, including pod existence checks, local pod retrieval, and bandwidth annotations
• Add unit tests for version package, including version adjustment and command parsing
• Update existing tests for credential clients and vswitch

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37.97%. Comparing base (94ffaf4) to head (2a4117e).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #861      +/-   ##
==========================================
+ Coverage   35.69%   37.97%   +2.27%     
==========================================
  Files         130      130              
  Lines       18919    18923       +4     
==========================================
+ Hits         6754     7186     +432     
+ Misses      11407    10928     -479     
- Partials      758      809      +51     

Flag	Coverage Δ
unittests	37.97% <100.00%> (+2.27%)	⬆️

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