Move structlog imports into a TYPE_CHECKING block to untie version bumps

[amoghrajesh]

Structlog released 25.5.0 version where structlog.dev.Styles was renamed as structlog.dev.ColumnStyles along with some refactoring. This breaks our CI like this:

  Stderr: Traceback (most recent call last):
    File "<string>", line 1, in <module>
    File "/home/runner/work/airflow/airflow/airflow-core/src/airflow/__init__.py", line 81, in <module>
      settings.initialize()
    File "/home/runner/work/airflow/airflow/airflow-core/src/airflow/settings.py", line 698, in initialize
      LOGGING_CLASS_PATH = configure_logging()
    File "/home/runner/work/airflow/airflow/airflow-core/src/airflow/logging_config.py", line 88, in configure_logging
      from airflow._shared.logging import configure_logging, init_log_folder, translate_config_values
    File "/home/runner/work/airflow/airflow/airflow-core/src/airflow/_shared/logging/__init__.py", line 27, in <module>
      from .structlog import configure_logging, init_log_file, init_log_folder
    File "/home/runner/work/airflow/airflow/airflow-core/src/airflow/_shared/logging/structlog.py", line 38, in <module>
      from .percent_formatter import PercentFormatRender
    File "/home/runner/work/airflow/airflow/airflow-core/src/airflow/_shared/logging/percent_formatter.py", line 29, in <module>
      from structlog.dev import ConsoleRenderer, Styles
  ImportError: cannot import name 'Styles' from 'structlog.dev' (/home/runner/work/airflow/airflow/.venv/lib/python3.10/site-packages/structlog/dev.py)

Move structlog imports into a TYPE_CHECKING block to untie version bumps

---

^ Add meaningful description above
Read the Pull Request Guidelines for more information.
In case of fundamental code changes, an Airflow Improvement Proposal (AIP) is needed.
In case of a new dependency, check compliance with the ASF 3rd Party License Policy.
In case of backwards incompatible changes please leave a note in a newsfragment file, named {pr_number}.significant.rst or {issue_number}.significant.rst, in airflow-core/newsfragments.

[ashb]

Lets see if TP's idea works

[amoghrajesh]

Just tried it 14be76e

[uranusjr]

We should remove the version bumps too.

[amoghrajesh]

Fair point, pushing a fix

[amoghrajesh]

That worked, thanks @uranusjr

[amoghrajesh]

Failing test is unrelated

[pankajkoti]

Thanks for the fix @amoghrajesh.

@kaxil wish to check if this would be included in 3.1.2 (not sure if we're still planning to cut one before you go on leave :))? Today, I observed with my local development efforts that upon installing Cosmos on 3.1.1 as base image, somehow structlog version gets updated (maybe via some cosmos dependency), and I observe this failure. I verified that Airflow 3.1.1 installs structlog 25.4.0, so I believe it's safe by itself.

[kaxil]

Yup, this will be part of 3.1.2. Has been chery-picked already to v3-1-test

[hynek]

Wow so sorry for that! To add some context from the structlog side: Styles wasn't really a thing – it was a hack to make the old-style class-variables-as-storage work as a type hint (I mean, what does Union[_Styles, Type[_Styles]] even mean). And since it was never documented, I kinda treated it like an internal thing.

Since you've already fixed it, I don't think it makes any sense to do any emergency releases form my side. Again, I'm sorry.

[amoghrajesh]

All good, @hynek!

I do not think any other project would've suffered it but we certainly did because Styles was exposed in the public interface, and we used it. IAC, we moved it rightly to a type checking block and I think we are good now.