feat: init anthropic agent (part 2) (#719)

.changeset/perfect-sloths-vanish.md

examples/anthropic/agent.ts

examples/toolsStream.ts

packages/core/e2e/fixtures/llm/open_ai.ts

packages/core/e2e/node/claude.e2e.ts

packages/core/e2e/node/fixtures/tools.ts

packages/core/e2e/node/openai.e2e.ts

packages/core/e2e/node/snapshot/agent.snap

packages/core/e2e/node/snapshot/agent_stream.snap

packages/core/e2e/node/snapshot/anthropic-agent.snap

packages/core/e2e/node/snapshot/gpt-4-turbo.snap

packages/core/e2e/node/snapshot/llm-anthropic.snap

packages/core/src/ChatHistory.ts

packages/core/src/agent/anthropic.ts

packages/core/src/agent/index.ts

packages/core/src/agent/openai/base.ts

packages/core/src/agent/openai/worker.ts

packages/core/src/agent/react/base.ts

packages/core/src/agent/react/worker.ts

packages/core/src/agent/runner/base.ts