feat:implement Distinct operator |test included

[Rich-T-kid]

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[Copilot]

Pull request overview

This PR implements a Distinct operator for the opti-sql-go query engine that filters input data to return only unique row combinations based on specified columns. The implementation follows the existing operator pattern in the codebase but contains several critical bugs related to memory management and resource cleanup that must be addressed before merging.

Key Changes:

• Adds a new Distinct operator struct with methods implementing the operators.Operator interface
• Implements a pipeline-breaking approach that consumes all input before returning distinct results
• Adds comprehensive test coverage including unit tests for the operator and helper functions

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 27 comments.

File	Description
src/Backend/opti-sql-go/operators/filter/limit.go	Implements the Distinct operator with helper functions for array manipulation and deduplication logic
src/Backend/opti-sql-go/operators/filter/limit_test.go	Adds test cases for Distinct operator functionality and helper functions including edge cases and resource management tests

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