add native Effect diagnostics API

[mattiamanzati]

Summary

• add a new native getEffectDiagnostics API hook that resolves a source file, ensures it is type-checked, and delegates Effect rule execution through an externally registered callback
• factor the existing checker-only Effect diagnostics flow into a shared internal/rulerunner so checker diagnostics and direct API calls use the same rule selection, directive handling, severity mapping, and override resolution
• register the API implementation through a new etsapihooks package, add a changeset, and generate a new shim/api package so the hook can be wired without importing TypeScript-Go internals directly

Validation

• pnpm setup-repo
• pnpm check
• pnpm lint
• full pnpm test not run