refactor(provider-core): add provider-core and provider-testing packages (#17299)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
9eea28bacdJulius Marminge committed on 10/8/2026, 9:18:16 PM· committed by GitHubparent5809487
64 files changedLine totals unavailable