Currently, the Siteinfo class uses formatversion=1.
This causes several issues:

• Boolean fields are returned as empty strings ("") or is missing instead of proper Booleans.
• Nested structures (namespaces, magicwords) need manual post-processing.
• '*' fields

The goal of this task is to migrate Siteinfo to formatversion=2 so that:

• All boolean values are returned by the API as True/False.
• _post_process fixes structure, no longer converts booleans.
• A backwards-compatible variant (siteinfo) remains for old scripts.
• A new site_info property provides raw formatversion=2 data