Refactor parametrized tests

[ashishpatel16]

The following test cases were redundant across test_LocalClassifierPerNode, test_LocalClassifierPerParentNode and test_LocalClassifierPerLevel -

• test_fit_1_class
• test_empty_levels
• test_fit_bert
• test_knn
• test_fit_multiple_dim_input
• test_predict_multiple_dim_input

This PR aims at using parametrized tests for executing these tests in a separate file test_LocalClassifiers, where all the common test cases should be written.

[codecov-commenter]

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Additional details and impacted files

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