Refactor: Add type hints to dashboard server functions

[pyob-bot]

Summary of Changes

• Added explicit type annotations to the is_port_available and run_server functions in src/pyob/dashboard_server.py.
• Updated is_port_available to specify an int input parameter and a bool return type.
• Updated run_server to specify a None return type.

Technical Impact

• Improves code readability and maintainability by providing clearer function signatures.
• Enhances static analysis and IDE autocompletion support, reducing the likelihood of type-related bugs during future development.