Add type hints to test_message.py

[SBNetto01]

What does this PR do, and why?

This PR adds the adequate type hints in each function from test_message.py, solving issue #1337

External discussion & connections

• [x] Discussed in #zulip-terminal in topic
• [x] Fully fixes #
• [ ] Partially fixes issue #
• [ ] Builds upon previous unmerged work in PR #
• [ ] Is a follow-up to work in PR #
• [ ] Requires merge of PR #
• [ ] Merge will enable work on #

How did you test this?

• [ ] Manually - Behavioral changes
• [ ] Manually - Visual changes
• [ ] Adapting existing automated tests
• [ ] Adding automated tests for new behavior (or missing tests)
• [x] Existing automated tests should already cover this (only a refactor of tested code)

Self-review checklist for each commit

• [x] It is a minimal coherent idea
• [ ] It has a commit summary following the documented style (title & body)
• [x] It has a commit summary describing the motivation and reasoning for the change
• [ ] It individually passes linting and tests
• [ ] It contains test additions for any new behavior
• [ ] It flows clearly from a previous branch commit, and/or prepares for the next commit

[neiljp]

@SBNetto01 Thanks for looking into this :+1:

Did you see the other PR for this? I think there is only one other?

Were you wanting feedback at this point, or unsure how to proceed given the failing linting/tests?

Do you understand why the linting and tests are failing? I'd be happy to discuss briefly here, or chat in more depth on chat.zulip.org if you need help with this.

[zulipbot]

Hello @zulip/server-refactoring members, this pull request was labeled with the "area: refactoring" label, so you may want to check it out!

[SBNetto01]

Thank you for your reply and sorry about the delay! I was waiting on some feedback, since the failed linting/tests are a bit weird. I wasn't able to use the --fix recommended on a few of the documentations, and all of them are related to "empty spaces" if I'm not mistaken, but it's not related to my modifications whatsoever. Would love to know how to proceed with this.