fix: #4651
This commit enhances the `prefer_namespace_keyword` rule in the
TypeScript linter: Add support for detecting and fixing nested module
declarations (e.g., module A.B {})
- Introduce helper functions `is_nest_module`, `is_valid_module`, and
`is_invalid_module` to improve code readability and maintainability
- Refactor the main `run` function to use these new helper functions
- Update test cases to cover nested module scenarios
- Improve error reporting for nested modules