feat(stac_cli): add unit testing infrastructure and core command tests

[Pratikdate]

Description

This PR adds a comprehensive unit testing layer to the stac_cli package and integrates it into the monorepo's CI pipeline. Key changes include:

• Infrastructure Set-up: Initialized the test/ directory within packages/stac_cli to manage command and utility tests.
• Environment Mocking: Added a mechanism to safely stub out required environment variables (like STAC_BASE_API_URL and STAC_GOOGLE_CLIENT_ID) during tests to prevent initialization crashes without real API keys.
• Core Command Tests: Implemented tests for BuildCommand, InitCommand, and DeployCommand to verify registration, name, and descriptions.
• Utility Reliability: Added tests for FileUtils to validate file system operations (create, read, delete) with automated sandbox cleanup.
• CI Pipeline Integration:
  • Added a test command to the root melos.yaml.
  • Updated .github/workflows/all_plugins.yaml to include a global test step for all packages.

Related Issues

Closes # (Insert issue number if applicable)

Type of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to change)
• Code refactor
• Build configuration change
• Documentation
• Chore

[CLAassistant]

All committers have signed the CLA.