chore: circumvents judge_config calls to make judge evaluations in optimization

[andrewklatzke]

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

Describe the solution you've provided

Updates the judges to fetch from .variation directly so we can avoid the warning stemming from the judge_config call when we're using our own history. Additionally, if we receive a message that is just a system message (new format) we'll just auto-append our user message with that data.

Describe alternatives you've considered

This is a fix/chore stemming from some updates to the base SDK.

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Note

Medium Risk
Changes how judge prompts are resolved for optimization runs (private SDK client access and custom interpolation); behavior should match intent but diverges from the public judge_config contract if flag shape or SDK rules differ.

Overview
Config judges in optimization no longer go through LDAIClient.judge_config. _judge_config now reads the judge flag via _client.variation, applies local {{key}} interpolation (including message_history and response_to_evaluate), and builds AIJudgeConfig itself so the SDK does not strip or warn on those reserved variables.

New-style judge templates that only define a system message get an automatic user turn built from optimization history and the response under test, so downstream _evaluate_config_judge still sees a full system/user conversation.

Tests mock raw flag variations instead of judge_config, and add coverage for system-only templates and template interpolation.

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