Enhance test coverage across entire codebase for codecov.

[MrKeiKun]

Description
This PR significantly enhances the test coverage across the entire tenv codebase to improve code quality metrics and ensure better reliability. The comprehensive test additions cover:

Changes Made

• New test files for all major packages including:
  • Core command packages (cmd/terramate/, cmd/tf/)
  • Configuration management (config/)
  • Package utilities (pkg/)
  • Version management system (versionmanager/)
• Updated dependencies in go.mod and go.sum to support enhanced testing

Test Coverage Areas

• API message handling (pkg/apimsg/)
• Architecture-specific code (pkg/archname/)
• Security and verification (pkg/check/cosign/)
• Download and file operations (pkg/download/, pkg/fileperm/)
• GitHub integration (pkg/github/)
• Compression utilities (pkg/uncompress/)
• Version management (builder, proxy, semantic versioning)
• Library examples and edge cases

Referenced Issue: #388

[MrKeiKun]

i think,i can say this is partial one. i wanna see pipeline though

[MrKeiKun]

Right now, total coverage is at least: 42.7%.

[kvendingoldo]

Checking your PR. I can take some time :)