refactor(pii): type NER payload and runtime boundaries

[binaryaaron]

Summary

• Adds typed NER API payloads and normalizes metadata serialization.
• Removes the PII replacer exclusion from ty checks.
• Types NER model, metadata, regex, and data-editor runtime boundaries.

Test plan

• mise run test -- tests/pii_replacer tests/data_processing/records/test_fragment.py
• mise run typecheck

Closes #614

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch binaryaaron/pr596-06-typecheck-pii

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