Modernize Documentation Theme with Furo

[Tejasrahane]

Fixes #12826

Changes Made

This PR modernizes the documentation theme by switching from Alabaster to Furo, a modern and clean Sphinx theme.

Updated pyproject.toml:

1. Added Furo theme and Sphinx-copybutton to the [dependency-groups] docs section:

   • "furo>=2024.1.29"
   • "sphinx-copybutton>=0.5.2" (optional UX enhancement)

2. Changed documentation theme from alabaster to furo

3. Added theme configuration with repository links:

   html_theme_options = {
       "source_repository": "https://github.com/TheAlgorithms/Python/",
       "source_branch": "master",
       "source_directory": "docs/",
   }
   

Benefits

• Modern, clean, and responsive design
• Better mobile support
• Improved navigation and search
• Dark mode support
• Enhanced copy button for code blocks