Add unit tests for internal/service module

[salignatmoandal]

What

This PR adds a comprehensive test suite for the internal/services module.

Why

• Improves code reliability and maintainability
• Makes future refactoring safer
• Provides documentation for expected behavior

Details

• Adds unit tests for:
  • Run()
  • CheckVersions()
  • listRemoteImages()
  • suggestUpdateCmd()
• Uses afero.NewMemMapFs() for in-memory filesystem testing
• Uses gock for HTTP request mocking
• Uses testify for assertions

Result

• Test coverage for the module is now above 90%
• All tests pass locally

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Let me know if you need any changes or improvements!