Add support for Python 3.12

[punchagan]

What does this PR do, and why?

Allows developing and installing zulip-terminal with Python 3.12.

External discussion & connections

• Discussed in #zulip-terminal in Support developing with Python 3.12 #T1541

How did you test this?

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

Self-review checklist for each commit

• It is a minimal coherent idea
• It has a commit summary following the documented style (title & body)
• 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

[Niloth-p]

I'm not familiar enough with dependency version management to review this, but I gave it a shot anyways.

• Just went through this list checking for any deprecations, and it looks like we're good on that front.

• Mypy ran into some errors when running linting for tests/.
  pytest imports numpy and exceptiongroup. Using:

if TYPE_CHECKING:
	from numpy import ndarray

And I get the error: Cannot find implementation or library stub for module named "exceptiongroup"/"numpy" [import-not-found]

I assume it's something to do with typing compatibility?

Github Actions must not have caught it since it does linting only on 3.8.
But, how come I'm getting them but you're not? Do you use PyPy or something, or am I doing something wrong? I tried with CPython 3.12.2.

[punchagan]

I'm not familiar enough with dependency version management to review this, but I gave it a shot anyways.

Thanks for taking the time to do the review!

But, how come I'm getting them but you're not? Do you use PyPy or something, or am I doing something wrong? I tried with CPython 3.12.2.

I'm using CPython 3.12.3 that comes with my distro. How did you setup 3.12.2? Can you share the full traceback?

[punchagan]

Duplicate #1379