Feat/vitest testing library msw

[D0dii]

Adding tests setup

• vitest
• react-testing-library
• msw

---

[!IMPORTANT] Introduces Vitest, React Testing Library, and MSW for testing with new test files, mock handlers, and configuration updates.

• Testing Setup:
  • Introduces vitest, react-testing-library, and msw for testing.
  • Adds vitest.config.mts for Vitest configuration with jsdom environment and setup files.
• Tests:
  • Adds plans-edit.test.tsx to test error handling in CreateNewPlanPage.
  • Adds plans.test.tsx to test error handling in PlanItem.
• Mocks:
  • Adds handlers.ts and server.ts for MSW mock server setup.
  • Mock handlers simulate API errors for departments, registrations, and course loading.
• Scripts:
  • Updates package.json scripts to include vitest commands for testing.
• Misc:
  • Adds error toast in app-sidebar.tsx for registration fetch failures.
  • Adds setup.ts for test environment setup with global mocks and server lifecycle management.

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[D0dii]

I know it isn't the prettiest code but for now I'm tired and don't have energy for it