siRNA featurizer bug?

[nouralmaa]

When adding new tests in tests/test_featurizer_kmer.py, transforming the siRNA featurizer raises an error. _extract_features_test in oligogym/features.py might be missing RNA strands and getting wrong k-mer counts

@pytest.mark.parametrize("featurizer", [kmer_merged()])
def test_feature_extraction_aso(featurizer):
    features = featurizer.fit_transform([ASO_TEST])
    features_sub = featurizer.transform([ASO_TEST])
    assert features.to_dict() == ASO_TEST_KMER_DICT
    assert features_sub.to_dict() == ASO_TEST_KMER_DICT


@pytest.mark.parametrize("featurizer", [kmer_merged(), kmer_split()])
def test_feature_extraction_sirna(featurizer):
    features = featurizer.fit_transform([SIRNA_TEST])
    if featurizer.split_strands:
        assert features.to_dict() == SIRNA_TEST_KMER_SPLIT_DICT
    else:
        assert features.to_dict() == SIRNA_TEST_KMER_MERGED_DICT

    features_sub = featurizer.transform([SIRNA_TEST])
    if featurizer.split_strands:
        assert features_sub.to_dict() == SIRNA_TEST_KMER_SPLIT_DICT
    else:
        assert features_sub.to_dict() == SIRNA_TEST_KMER_MERGED_DICT