Consider adding LLM support for draft_validation

Prework

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• Search for duplicates among the existing issues (both open and closed).

Proposal

Describe the new feature clearly and concisely. If applicable, write a minimal example in R code or pseudo-code to show input, usage, and desired output.

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Consider adding ellmer-based LLM support for draft_validation(), similar to Python library capabilities (https://posit-dev.github.io/pointblank/user-guide/draft-validation.html). Similar could apply to future LLM-powered validation data dictionary generation. Please feel free to ignore if this is outside of scope.