[Feature] Add a `.markdown()` function for response

[perkfly]

Extract LLM-friendly markdown text from response.

Is your feature request related to a problem? Please describe. N/A

Describe the solution you'd like

from curl_cffi import requests

r = requests.get("https://example.com/content-20240704.html")

text = r.markdown()

Describe alternatives you've considered N/A

Additional context Dependeices should be optional, probably with pip install curl-cffi[extra]