feat: implements template/raw methods for fetching configs

[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

Related issues

https://launchdarkly.atlassian.net/jira/software/c/projects/AIC/boards/2045?selectedIssue=AIC-2843

Describe the solution you've provided

Implements three methods:

• completion_config_template
• agent_config_template
• judge_config_template

To mirror the base names. Each of these retrieves the config without running the interpolation process.

Describe alternatives you've considered

Alternatively users can use the base .variation method to retrieve the config, but then things like typing are foisted onto the consumer rather than the SDK itself. We're opting to add a method so that users still receive the niceties (tracker, types).

Additional context

Add any other context about the pull request here.

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Note

Low Risk
Additive SDK surface with default interpolation unchanged; behavior change is isolated to new template methods and optional interpolate=False paths.

Overview
Adds completion_config_template, agent_config_template, and judge_config_template on LDAIClient so callers get the same typed configs and trackers as the existing *_config APIs, but with Mustache placeholders left unrendered in message content / instructions (including judge reserved {{message_history}} / {{response_to_evaluate}} when using the judge template path).

Internal evaluation now accepts an interpolate flag (default true) so __evaluate skips chevron rendering when false; the template methods call with variables=None and interpolate=False. Each template method emits a dedicated $ld:ai:usage:*-config-template track event.

New test_config_template.py covers placeholder preservation, parity with rendered configs, tracking, and defaults.

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