Automated weights column checks through Mixin Class and capturing shared weight tests in generic test classes

[Ritunjai-Sharma]

The following work has been done as part of this PR:

1. WeightColumnMixin mixin class created in a new file mixins.py with check_weights_column method to replace check_weights_column method in base.py: Commit 4bff09e3. Note that post implementing this check_weights_column check for weighted transformers, some tests for nominal transformers failed since the testing data was using null values in weight column, which logically shouldn't be allowed. This testing data has been updated to not contain null values in weight column.

2. Refactored testing of weighted transformers to move shared tests in generic testing classes: Commit 43827aad. As part of this, the following work was done:

   1. Created WeightColumnInitTests class with test to check that the weight is str or None. Consequently, test_weight_arg_errors and test_weight_value_type_error tests removed from test_MedianImputer.py and test_ModeImputer.py. Similar test in mean imputer not touched for now (test should be removed as part of mean imputer test overhaul ticket: Bring MeanImputer in line with new testing setup #208)
   2. Added test_weight_arg_errors to GenericCappingInitTests class of test_BaseCappingTransformer.py to check that the weight is str or None for CappingTransformer and OutOfRangeNullTransformer.
   3. Added generic weight testing classes GenericImputerFitTestsWeight and GenericImputerTransformTestsWeight to test_BaseImputer.py and removed duplicated fit and transform weight tests in test_MedianImputer.py and test_ModeImputer.py

[limlam96]

FYI getting some conflicts :)

[limlam96]

can you update changelog plz :)

[Ritunjai-Sharma]

FYI getting some conflicts :)

I've fixed the merge conflicts and post merge conflict resolution linting issues in commits: 32ea5f09, f686809 and 6ad2053

[Ritunjai-Sharma]

can you update changelog plz :)

Yes! Done here: abdc10b

[limlam96]

looks good, nice work RJ!