Support cost estimation before execution and improve configuration

[shaoyijia]

The default configurations in the Readme.md are corresponding to our hyper-parameters setup in the NAACL'24 paper.

As people are using/building on top of this project, having cost estimation (maximum number of call to language model, maximum number of call to search engine/retriever) is necessary.

[shaoyijia]

Currently, we provide a profiling function after processing a topic. You can call summary() to see the time, model usage for each step. Run reset() before starting a new topic.