refactor lists_json_get in prep for fastapi

[RayBB]

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[RayBB]

AI review

Summary: Refactors lists_json_get in openlibrary/plugins/openlibrary/lists.py to prepare for FastAPI migration.
Changes:

1. Renamed get_lists → get_lists_data and made it a @staticmethod
2. Changed from using web.ctx.path to accepting path as a parameter
3. Cleaned up input validation to use local variables instead of modifying i object
   Risks: LOW

• No breaking changes: The old get_lists method wasn't called externally - only internally in this class (lines 507, 510). Other get_lists references in the file (lines 258, 288, 298, 516, 1045) are different methods on user, mb.user, doc objects.
• Functional equivalence: The new static method does the exact same thing, just with better separation of concerns.
• Input validation preserved: The limit cap (max 100) and offset floor (min 0) logic remains intact.
  This is a clean refactor - no functional changes, just code organization improvements for future FastAPI compatibility.