feat: abstract query type (#1052)

.changeset/strange-pumas-whisper.md

examples/lowlevel.ts

packages/core/package.json

packages/core/src/query-engine/base.ts

packages/core/src/query-engine/index.ts

packages/core/src/schema/index.ts

packages/core/src/schema/type/engine–response.ts

packages/core/src/utils/llms.ts

packages/llamaindex/src/QuestionGenerator.ts

packages/llamaindex/src/agent/base.ts

...llamaindex/src/engines/chat/CondenseQuestionChatEngine.ts

packages/llamaindex/src/engines/chat/ContextChatEngine.ts

packages/llamaindex/src/engines/chat/SimpleChatEngine.ts

packages/llamaindex/src/engines/chat/types.ts

...ages/llamaindex/src/engines/query/RetrieverQueryEngine.ts

packages/llamaindex/src/engines/query/RouterQueryEngine.ts

...es/llamaindex/src/engines/query/SubQuestionQueryEngine.ts

packages/llamaindex/src/engines/query/types.ts

packages/llamaindex/src/evaluation/Correctness.ts

packages/llamaindex/src/evaluation/Faithfulness.ts