Refactor: src/screens/UserPortal/Chat from Jest to Vitest

[VanshikaSabharwal]

Is your feature request related to a problem? Please describe.
This file is currently tested using Jest. As part of our migration to Vitest, we need to refactor this file's test cases to align with Vitest's syntax and features.

Acceptance Criteria

1. Replace Jest-specific functions and mocks with Vitest equivalents
2. Ensure all tests in src/screens/UserPortal/Chat pass after migration using npm run test:vitest
3. Maintain the test coverage for the file as 100% after migration
4. Upload a video or photo for this specific file coverage is 100% in the PR description

Additional context

• Refer to the merged PR for the base Vitest configuration:
  https://github.com/PalisadoesFoundation/talawa-admin/pull/2457/files#diff-9a5a35cf8d7f02b2bba90905714b762560579c4789e9eb4cebb4607980aa3d93
• Vitest documentation:
  https://vitest.dev/

Potential internship candidates

Please read this if you are planning to apply for a Palisadoes Foundation internship

• Student Internship Programs talawa#359

[NishantSinghhhhh]

@palisadoes @varshith257 , can you please assign this issue to me , I want to work on this one too

[palisadoes]

@NishantSinghhhhh Over the past 2 weeks you have closed 7 PRs without reviews.

We have a policy of unassigning contributors who close PRs without getting validation from our reviewer team. This is because:

1. We start looking for people to review PRs when you submit them.
2. We often contact them and link to the PR. If the PR is closed the whole effort is wasted.
3. The historical thread of reviewer comments is broken when the work is spread across multiple PRs. The quality of our code is affected negatively.

Please be considerate of our volunteers' limited time and our desire to improve our code base.

This policy is stated as a pinned post in all our Talawa repositories. Our YouTube videos explain why this practice is not acceptable to our Community.

Unfortunately, if this continues we will have to close the offending PR and unassign you from the issue.