Add getInstanceWithProviders() utility for testing services with dependencies

[Paratron]

I am currently introducing testing-library for angular with vitest at our company and learned that while there is the very handy render() function in testing-library, an alternative for testing services or facades with injections did not exist.

I added a small new function getInstanceWithProviders() to the library which simplifies dependency injections into services or facades.

Example

@Injectable()
class DatabaseService {
  getData() {
    return 'real data';
  }
}

@Injectable()
class UserService {
  private db = inject(DatabaseService);

  getUser() {
    return `User: ${this.db.getData()}`;
  }
}

// Test with mocked dependency
it('should inject a mock service into a service that depends on it', () => {
  const mockDatabase = { getData: () => 'mock data' };
  
  const userService = getInstanceWithProviders(UserService, [
    { provide: DatabaseService, useValue: mockDatabase }
  ]);

  expect(userService.getUser()).toBe('User: mock data');
});

I have already created a test file for the new function and can also provide an example in the example project if this addition to the library is desired.