Fix Read the Docs build failures

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.

Start with docs/conf.py and .readthedocs.yaml, especially the fail_on_warning setting, then inspect how the missing modules.rst and multibase.rst files are expected to be generated. Run the Read the Docs documentation build and verify it completes without warnings from the deprecated settings or missing API documentation files.