[evaluation] fix: Mark GroundednessEvaluator.has_evaluator as private

[kdestin]

Description

This pull request marks GroundednessEvaluator.has_context as "private".

All SDK Contribution checklist:

• 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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Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull Request Overview

This pull request marks the has_context method in the GroundednessEvaluator class as private by renaming it to _has_context. This is a code cleanup change that improves encapsulation by hiding an internal utility method from the public API.

• Renames has_context method to _has_context to make it private
• Updates the method call reference to use the new private method name

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

azure-ai-evaluation