Created the tests for the navbar interactor

[Adish-Singh]

Summary
This pull request introduces a complete JUnit test suite for the NavbarInteractor, along with a mock presenter implementation (NavbarMockPresenter). These tests ensure that navigation requests made through the interactor are correctly delegated to the corresponding presenter methods defined in NavbarOutputBoundary.

Key Additions

1. NavbarInteractorTests

• A new test class containing the following:
  - Individual tests for each navigation method:
  - switchToLogin
  - switchToSignUp
  - switchToCommunity
  - switchToGenerateRecipe
  - switchToApproveRecipe
  - switchToProfile
  - switchToGroceryList
  - switchToMealPlan
  - switchToSearchByIngredients
  - switchToLikedRecipeList
• A sequential test verifying correct behavior when multiple navigation commands are issued consecutively.
• Assertions ensure that the interactor routes calls to the correct presenter method.

2. NavbarMockPresenter

• A lightweight mock implementation of NavbarOutputBoundary enabling verification of interactor behavior:
  - Tracks the last view switched via a lastViewSwitched field.
  - Provides getter for test assertions.
  - Implements all navigation methods expected by the interactor.

Motivation
The navigation system is a key component of the application's user flow.
Prior to this PR, the NavbarInteractor lacked automated tests, leaving its correctness unverified.
This addition improves:
- Reliability of navigation handoff logic
- Confidence in future refactoring
- Compliance with clean architecture testing principles

Testing
All tests pass successfully.
I also checked for 100% line coverage for the interactor.

Files Added
src/test/java/use_case/nav_bar/NavbarInteractorTests.java
src/test/java/use_case/nav_bar/NavbarMockPresenter.java

Impact
No production code is modified.
This PR enhances test coverage and ensures the navigation interactor behaves as designed.

[matthew-SG]

Yeah that makes sense. Appreciate you writing the tests.