Validates that few-shot examples in a LangExtract.Template are self-consistent.

Each extraction text should align exactly against its own example's source text. Catches typos, hallucinated spans, and copy-paste errors before they reach the LLM.

Deliberately uses the production Alignment.Aligner, so a passing validation predicts how the same extractions align at runtime.

The validator is a pure function — it reports what it finds. The caller decides what to do with the results (log, raise, ignore).