Fix Read the Docs build failures

[acul71]

The Read the Docs documentation build is currently failing due to:

1. Deprecated Sphinx configuration settings in docs/conf.py:

   • source_suffix = '.rst' should be source_suffix = {'.rst': 'restructuredtext'}
   • master_doc = 'index' should be root_doc = 'index'

2. Missing API documentation files (modules.rst and multibase.rst) that need to be generated before the build.

These issues cause warnings that fail the build because fail_on_warning: true is set in .readthedocs.yaml.

This issue tracks the fix for the documentation build process.