feat: move agent into core (#1254)

packages/core/package.json

packages/core/src/agent/base.ts

packages/core/src/agent/index.ts

packages/core/src/agent/llm.ts

packages/core/src/agent/types.ts

packages/core/src/agent/utils.ts

packages/core/src/global/index.ts

packages/core/src/global/settings.ts

packages/core/src/global/settings/callback-manager.ts

packages/core/src/objects/index.ts

packages/core/src/utils/index.ts

packages/core/tests/agents.test.ts

packages/core/tsconfig.json

packages/env/src/index.browser.ts

packages/env/src/index.edge-light.ts

packages/env/src/index.ts

packages/env/src/index.workerd.ts

packages/env/src/logger/index.ts

...maindex/e2e/examples/cloudflare-worker-agent/package.json

...maindex/e2e/examples/cloudflare-worker-agent/src/index.ts