feat: add `llm-stream` event (#707)

apps/docs/docs/recipes/cost-analysis.mdx

examples/package.json

examples/recipes/cost-analysis.ts

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

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

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

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

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

packages/core/e2e/node/utils.ts

packages/core/src/callbacks/CallbackManager.ts

packages/core/src/llm/LLM.ts

packages/core/src/llm/anthropic.ts

packages/core/src/llm/mistral.ts

packages/core/src/llm/ollama.ts

packages/core/src/llm/open_ai.ts

packages/core/src/llm/types.ts

packages/core/src/llm/utils.ts

pnpm-lock.yaml