[PECOBLR-201] add variant support

[shivam2680]

Description

This pull request introduces support for detecting and handling VARIANT column types in the Databricks SQL Thrift backend, along with corresponding tests for validation.
updated the _col_to_description and _hive_schema_to_description methods to process metadata for VARIANT types
Added unit and end-to-end tests to ensure proper functionality.

Testing details

End-to-End Tests:

• Added tests/e2e/test_variant_types.py to validate VARIANT type detection and data retrieval. Includes tests for creating tables with VARIANT columns, inserting records, and verifying correct type handling and JSON parsing.

Unit Tests:

• Tests cover scenarios like VARIANT type detection, handling of null or malformed metadata, and fallback behavior for missing Arrow schemas.

[github-actions]

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[github-actions]

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[github-actions]

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[github-actions]

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[jprakash-db]

can you plz incorporate @pytest.mark.parametrize , I feel a lot of test code duplication can be avoided

[github-actions]

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[shivam2680]

The test_thrift_backend class inherits from unittest.TestCase, which is designed for unittest's test discovery and execution model. When you use @pytest.mark.parametrize with a unittest.TestCase class:

• Pytest creates separate test instances for each parameter set
• Unittest's test runner doesn't understand these parametrized arguments
• Result: TypeError: missing required positional arguments

[jprakash-db]

LGTM. Thanks for making the changes