Make the default value of n_features match the khiops core value

[tramora]

• KhiopsClassifier, KhiopsRegressor, KhiopsEncoder

Fixes #543

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[folmos-at-orange]

Update the changelog.

[tramora]

Update the changelog.
Fixed

[popescu-v]

I'd add n_features to the monotable tests (e.g. in test_parameter_transfer_classifier_fit_from_monotable_dataframe), in which case the expected max_constructed_variables should equal the value of n_features set in the test.

[tramora]

After exchanging with @folmos-at-orange on this PR or the other one related, the idea here is to verify the core parameter is set at its default value (1000) WITHOUT giving the optional input n_features.
Otherwise it would only be checking the correspondance between the value passed to the sklearn estimators and the value passed to the core

[popescu-v]

Idem above.

[popescu-v]

Idem above.

[popescu-v]

A few minor changes in the tests (see the comments).