1. Extract `PyKustoClientBase` class which is inherited by `PyKustoClient` and `PySparkKustoClient`.
2. Remove dependency of `PySparkKustoClient` on azure-kust-data package.
3. Add `pyspark` installation option, for installing without dependencies which are not needed in PySpark.
4. Replace `tests_require` (which is deprecated) with `extras_require`.
5. Small improvement to test coverage exclusion style.
Yonatan Most