style: flake8 violation F401

[fscnick]

Why are these changes needed?

While running the pre-commit hook of flake8, the following error occurs if Python version is 3.12. It's because the version of flake8 is too old.

./python/ray/experimental/channel/nccl_group.py:13:5: F401 'cupy as cp' imported but unused
./python/ray/tests/autoscaler_test_utils.py:5:1: F401 'typing.Callable' imported but unused
./rllib/evaluation/sampler.py:58:5: F401 'gymnasium.envs.classic_control.rendering.SimpleImageViewer' imported but unused

However, there are another violation appeared after removing these unused import.

python/ray/experimental/channel/nccl_group.py:91:37: F821 undefined name 'cp'
python/ray/tests/autoscaler_test_utils.py:46:55: F821 undefined name 'Callable'
rllib/evaluation/sampler.py:343:35: F821 undefined name 'SimpleImageViewer'

After taking a look,
nccl_group.py:91 and sampler.py:58 are used in Optional
autoscaler_test_utils.py:46 Callable is used in type comment.

Thus, suppress F401.

Related issue number

Closes #48062

Checks

• I've signed off every commit(by using the -s flag, i.e., git commit -s) in this PR.
• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
    corresponding .rst file.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[fscnick]

@MortalHappiness PTAL

[Daraan]

Disclaimer: I am just some random person showing up here.

As the minimum version is now 3.9 and PEP 585 is available. typing.Dict, typing.Callable and similar are deprecated.

Now we can (and should rather) use from collections.abc import Callable and the builtins dict instead, if we do not care about backward compatibility

Suggested change

	self.cmd_to_callback: Dict[str, Callable] = cmd_to_callback or {}
	self.cmd_to_callback: dict[str, Callable] = cmd_to_callback or {}

[MortalHappiness]

You're right. However, since our Python worker in CI is still on Python 3.8, we cannot change this now. I'm still waiting for our CI team to upgrade the worker to Python 3.9. Additionally, many places still use typing.Dict as a type annotation. We can use tools to update it to the new syntax after the Python worker version is upgraded.

[MortalHappiness]

Close this because we decide to migrate from flake8 to ruff instead of upgrading flake8.