/claim #560

Add unit tests for database operations including column types, owned columns, arithmetic operations, comparison operations, indexing, grouping, ordering and union utilities

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Rationale for this change

Improve test coverage for database utility modules

What changes are included in this PR?

• arrow_schema_utility.rs - schema conversion and field preservation tests
• column_arithmetic_operation.rs - arithmetic operations across integer types
• column_comparison_operation.rs - comparison operations and type validation
• column_index_operation.rs - indexing operations
• column_type.rs - type conversions and bit handling
• group_by_util.rs - aggregation operations with sum and max
• order_by_util.rs - sorting and ordering comparisons
• owned_column.rs - basic column operations like empty checks and slicing
• table_ref.rs - table reference validation
• union_util.rs - union operations for various column types

Are these changes tested?

Yes.