Change the read the docs template from furo to sphinx-book-theme

[sweep-ai[bot]]

@edreisMD I have started working on this PR to change the readthedocs template to sphinx-book-theme. The files I plan to modify are:

• docs/conf.py: Change the html_theme and add theme options for sphinx-book-theme.
• docs/conf.py: Remove the custom CSS file reference.
• docs/conf.py: Add sphinx_book_theme to the extensions list.

Give me a minute!

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