test: add unit tests for hooks nav2_hook module

[Wanbogang]

Summary

This PR adds comprehensive unit tests for the src/hooks/nav2_hook.py module to improve code coverage and ensure the stability of the start_nav2_hook and stop_nav2_hook functions.

Changes

• Added tests/test_hooks_nav2_hook.py with tests for:
  • start_nav2_hook function (success, HTTP error, client error)
  • stop_nav2_hook function (success, HTTP error, client error)
• Properly mocks the aiohttp.ClientSession and related components for testing
• Includes helper functions to reduce code duplication in tests
• Uses pytest and unittest.mock for asynchronous mocking

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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