Improve logic in src/document directory
- Add safety check in cleanDocFn to prevent accessing .type on non-object contents
- Refactor stripTrailingHardlineFromParts to cache array lookups for better readability
- Improve isEmptyDoc function clarity by making the control flow more explicit
- Add explicit type checking before accessing nested group properties
Co-authored-by: fisker <172584+fisker@users.noreply.github.com>
