add feature_names_in_ and n_features_in_ attributes to dummy estimators

[tvdboom]

Reference Issues/PRs

Fixes #27907

What does this implement/fix? Explain your changes.

Add the attributes feature_names_in_ and n_features_in_ to the Dummy estimators.

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[tvdboom]

The PR fails on a single test because the error type is now different (IndexError instead of ValueError). the test is the following:

def test_quantile_strategy_empty_train():
    est = DummyRegressor(strategy="quantile", quantile=0.4)
    with pytest.raises(ValueError):
        est.fit([], [])

Not sure if I can just change the error type in the test because I am unsure what the test is actually testing (that it fails or that a specific error is raised).

[adrinjalali]

I think it'd make sense to fix the test, the behavior is now more consistent with the other estimators. It would need a changelog entry though.

[yuanx749]

Some nitpicks.

[tvdboom]

@yuanx749 can you review again?

[yuanx749]

@yuanx749 can you review again?

I just came across this PR and think it is good. But I am not a maintainer, so you need to ask a maintainer to approve. Sorry for the confusion...

[tvdboom]

I see. @adrinjalali can you review?

[adrinjalali]

This needs a test to make sure the attributes are correctly added to the estimator instance. Otherwise LGTM

[adrinjalali]

Otherwise LGTM.

[tvdboom]

@adrinjalali can this be merged?

[thomasjpfan]

Thank you for the PR @tvdboom ! LGTM