NOISSUE - Add manager tests

[SammyOina]

What type of PR is this?

What does this do?

• New Features

  • Introduced new unit tests for managerService and ManagerClient functionalities, enhancing test coverage.
  • Added tests for QEMU configuration and persistence methods, ensuring correct command-line argument generation and VM state management.

• Bug Fixes

  • Improved handling of context cancellation in gRPC server methods to enhance robustness.

• Documentation

  • Added code generation directive for creating mock implementations of the Service interface.

• Refactor

  • Enhanced existing test functions for better error handling and coverage across various scenarios.

Which issue(s) does this PR fix/relate to?

• Related Issue #159

Have you included tests for your changes?

Did you document any new/modified feature?

Notes

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 44.11765% with 38 lines in your changes missing coverage. Please review.

Project coverage is 26.32%. Comparing base (3d9fde3) to head (6773f6d).

Files with missing lines	Patch %	Lines
manager/mocks/service.go	38.46%	17 Missing and 15 partials :warning:
manager/api/grpc/server.go	62.50%	5 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #273 +/- ## ========================================== + Coverage 18.83% 26.32% +7.48% ========================================== Files 76 77 +1 Lines 5213 5273 +60 ========================================== + Hits 982 1388 +406 + Misses 4057 3656 -401 - Partials 174 229 +55 ```

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