[evaluation] fix: Honor renmed columns for aoai column mapping

[kdestin]

Description

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
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• Pull request includes test coverage for the included changes.

[Copilot]

Pull Request Overview

This PR fixes an issue in the Azure OpenAI evaluation module where column mappings were not properly honoring renamed columns during data source processing. The change refactors the column mapping logic to use a proper data structure and fixes the nested value insertion to use the correct destination column name.

Key Changes

• Introduces a ColumnMapping NamedTuple to better structure column mapping data
• Fixes the nested dictionary insertion to use the destination column name instead of the source column name
• Modernizes string processing with removeprefix() and removesuffix() methods

[Copilot]

This line uses mapping.destination_column as the key, but it should use the last segment of the value path (mapping.value_path[-1]) to maintain the correct nested structure. The destination column name is meant for the overall mapping, not the leaf key in the nested dictionary.

Suggested change

	cursor[mapping.destination_column] = str_val
	cursor[mapping.value_path[-1]] = str_val