[ENH] Improve Global Config Architecture

[satvshr]

Metadata

• Reference Issue: fixes [ENH] Improve Global Config Architecture #1564
• New Tests Added: No
• Documentation Updated: No
• Change Log Entry: Replaces global variables with an instance of a dataclass OpenMLConfig.

Details

• What does this PR implement/fix? Explain your changes.
  Refactors the configuration handling to centralize state in a single OpenMLConfig.

• Why is this change necessary? What is the problem it solves?
  This simplifies configuration management and makes it easier to add validation and consistency checks, avoiding scattered logic and direct mutation of module-level globals.

[jgyasu]

Can you please add more details in your PR description?

[satvshr]

It's not ready for review yet! Hence a draft.

[satvshr]

@SimonBlanke if we make the dataclass OpenMLConfig frozen, we will have to change everything from the current openml.config._config.cachedir = _root_cache_directory to _config = replace(_config, cachedir=_root_cache_directory), it is your call. In my opinion, it is a good idea to freeze it and use _config = replace(_config, cachedir=_root_cache_directory) everywhere (hence making it immutable) while I try to find a better fix to the problem.

For anyone else trying to help out, kindly refer to the issue attached to the PR (#1564) to get into the loop on the discussion.

ps: Even though this is a temporary fix it seems like a good step in the right direction for having a proper config. I think I would like to add and remove a few things to build on top of this once ive a better idea though (and once this PR is closed).

[codecov-commenter]

Codecov Report

❌ Patch coverage is 68.35443% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.54%. Comparing base (bd8ae77) to head (7c82054).

Files with missing lines	Patch %	Lines
openml/config.py	67.74%	20 Missing ⚠️
openml/cli.py	0.00%	2 Missing ⚠️
openml/testing.py	71.42%	2 Missing ⚠️
openml/_api_calls.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1577      +/-   ##
==========================================
+ Coverage   79.14%   79.54%   +0.39%     
==========================================
  Files          36       36              
  Lines        4320     4316       -4     
==========================================
+ Hits         3419     3433      +14     
+ Misses        901      883      -18     

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