Add id to users with same name

[Sushmey]

What does this PR do?
On the Zulip terminal, users with same name weren't discernable because they were considered the same users. This PR compares users based on their user id and then displays the user id beside their user name if they have the same user name.

Fixes #1151

Tested?

• Manually
• Existing tests (adapted, if necessary)
• New tests added (for any new behavior)
• Passed linting & tests (each commit)

Commit flow
first commit -> comparing users based on user_id instead of name so that a separate header can be displayed

second commit -> displaying user_id beside all the users who have same name as more than one user in the list of all users. Adding a new style class so that the appended user_id doesn't look like a part of the username

third commit -> changing label from names to msg_sender in all colour themes

Notes & Questions
This makes users with same name have different headers by appending the id to the author name and shows it as a visually separate addition.

Interactions

• Waiting on PR review

Visual changes
Before:

After:

[mounilKshah]

I ran your code manually and it worked fine for me. I tried going through the files to give an in-depth review, but it is difficult to review due to the current commit structure. It would be great if you could squash the commits using git rebase.
Also, upon running pytest on your PR, there were errors. All those can be looked into deeper once the commit structure is streamlined.

[neiljp]

@Sushmey Ah, I'm also finding the tests are failing locally, so that may have been a migration issue on my part.

I also meant to say that the last commit doesn't have test changes and clearly changes behavior, which is one reason I'd like to see a new test for previous commit, so that the code change can match a test change.

[Sushmey]

@neiljp Thank you so much for the review! 🤗

I've made changes based on your comments.

I added a separate test for duplicate usernames but different author ids to account for the new behaviour and updated a test case for the same. I tried including it in the same test but it doesn't seem possible without having to change every test case parameter. Also, added a mock response as false for the is_user_name_duplicate function so that it doesn't fail for the reasons mentioned earlier, and since duplicate usernames aren't what we are testing in that test anyway.