feat: add AI Config judge support

[knfreemLD]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

See https://docs.google.com/document/d/1lzYwQqCcTzN_2zkxJZDfJtgUcEJ4jbpx0KSsJ2bRENw/edit?tab=t.0#heading=h.5d8l30brvyuw for context

For other SDK implementations, see:

• feat: Added custom judge support for ai configs js-core#1073
• feat: add support for custom judges via evaluation metric key python-server-sdk-ai#86 & feat: Add Chat and Judge supporting methods python-server-sdk-ai#64

Describe the solution you've provided

Extending the Go SDK to support AI Config evaluations. This includes custom evaluator support as well.

This SDK was written with hopes to be congruent with the python and node implementations. Changes were verified by a local app that was created; the resultant data can be observed in the evaluator metrics for this AI config.

Describe alternatives you've considered

Provide a clear and concise description of any alternative solutions or features you've considered.

Additional context

Add any other context about the pull request here.

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Note

Medium Risk
Adds new evaluation and metric-tracking paths (including dynamic metric keys and new event payload fields), which could affect analytics correctness and runtime behavior if misconfigured. Changes are well-covered by tests but touch core SDK tracking surfaces.

Overview
Adds judge-mode support to AI Configs by extending the config datamodel and builder with mode, evaluationMetricKey/evaluationMetricKeys, and judgeConfiguration (with defensive copying to keep configs immutable).

Introduces Client.JudgeConfig to fetch judge configs while preserving {{message_history}} / {{response_to_evaluate}} placeholders for a second Mustache interpolation pass during evaluation, and adds a new ldai/judge package that samples, interpolates, invokes a structured provider, and parses judge responses.

Extends Tracker with TrackJudgeResponse to emit evaluation scores as metrics (including optional judgeConfigKey in event data), and adds comprehensive tests covering parsing, placeholder preservation, schema generation, sampling, and response validation.

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Cursor Bugbot has reviewed your changes and found 2 potential issues.