Layers 208–221, Python 3.13, pyproject.toml, experimental download boost

Updated API schema through layers 208, 214, 216, 221.

• Added use_experimental_download_boost client flag.
• Added Python 3.13 support.

• Migrated to pyproject.toml, dropped setup.py / tox.ini / requirements.txt.
• Dropped Python 3.8 support.
• Updated project metadata.

• Fixed docs generation.
• Fixed raw docs description generation.
• Fixed raw base docs.
• Fixed type hinting on raw methods.
• Fixed CodeQL workflow permissions notice.