Improve unit tests across the repository

[mouismail]

Implements comprehensive unit tests across the repository to improve test coverage and validate critical functionalities.

• GitHub and GitLab Integration Tests: Adds actual test cases with assertions for GetRepos functions in github/github_test.go and gitlab/gitlab_test.go, utilizing mock HTTP servers to simulate API responses. Tests validate successful data retrieval and error handling for both GitHub and GitLab repositories.
• Readme and Stats Package Tests: Implements test cases in pkg/readme/readme_test.go and pkg/stats/stats_test.go to validate file operations and the functionalities of the Table struct, including table creation, row addition, and string representation.
• Bitbucket Package Tests: Introduces unit tests for the bitbucket package in bitbucket/bitbucket_test.go, testing the GetRepos function with a mock HTTP server to simulate Bitbucket API responses and validate repository parsing and error scenarios.
• Command Package Tests: Adds unit tests for the cmd package in cmd/root_test.go and cmd/start_test.go, testing command execution, argument parsing, and flags parsing for the root and start commands.

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