Add scikit-learn metadata routing support to BaseRegressor

[yousefkhedr777]

//notes
-i think metadata is the best way because implements metadata routing for the geometry parameter within the BaseRegressor class because no existing public APIs were changed and users not relying on Pipeline or GridSearchCV are unaffected and existing workflows continue to work as before
-This change is designed for scikit-learn ≥ 1.3, where metadata routing is supported.
Older versions of scikit-learn are not affected by this change.

Key changes:

• add get_metadata_routing() to BaseRegressor to explicitly declare geometry as required metadatas.
• Declared geometry as a required metadata input to be only keyword to avoids misuse in preprocessing steps for:
  • fit
  • predict
  • score
• Ensured compatibility with Scikit-Learn's Pipeline and GridSearchCV when enable_metadata_routing=True is configured.

Verified the logic using a mock estimator to ensure metadata is correctly routed through a Pipeline.

[theralavineela]

Just a heads-up based on earlier discussions: this relies on scikit-learn’s metadata routing (MetadataRequest, _fit_context), which is still experimental/private .It might be safer to avoid this for now and stick to explicit geometry handling until the API stabilises :)

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.22%. Comparing base (7f5a1c7) to head (f1f00fd).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
gwlearn/base.py	83.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #77      +/-   ##
==========================================
- Coverage   91.36%   91.22%   -0.15%     
==========================================
  Files           6        6              
  Lines         799      809      +10     
==========================================
+ Hits          730      738       +8     
- Misses         69       71       +2     

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[martinfleis]

What is it you're actually doing here, besides polluting the PR with your .idea folder?