feat(weave_ts): add provider name to turns

[rgao-coreweave]

Summary

• add optional typed providerName state to the TypeScript Turn API
• accept it through startTurn() / Conversation.startTurn() and Turn.record()
• emit it as gen_ai.provider.name on the root invoke_agent span at Turn.end()
• update the Claude Agent SDK integration to pass providerName when creating its turn instead of calling setAttributes()
• cover initial, recorded, and preserved provider values in Turn tests

Testing

• pnpm exec jest --runInBand src/__tests__/genai/turn.test.ts src/__tests__/integrations/claude-agent-sdk/otelTracer.test.ts — 25 passed
• pnpm test — 455 passed
• pnpm run typecheck:cjs — passed
• pnpm run typecheck:esm — passed
• pnpm run prettier-check — passed
• targeted ESLint — passed

Breaking changes

None. providerName is optional and defaults to an empty string.

Related

TypeScript parity for the Python Turn provider support in #7654. This PR is independent and based directly on master.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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