Replace lazyproperty with functools.cached_property

[KRRT7]

Summary

• Replace custom lazyproperty descriptor with stdlib functools.cached_property
• Fix bug where 26 properties returning None were re-evaluated on every access instead of caching — lazyproperty.__get__ uses if value is None to detect a cache miss, so any property that legitimately returns None re-runs on every access
• Slight performance improvement on cached reads — cached_property is a non-data descriptor, so after first access the __dict__ entry shadows the descriptor directly (plain dict lookup vs __get__ call)
• Nothing in the codebase ever assigns to a lazyproperty-decorated attribute, so dropping the write-protection from the data descriptor has no behavioral impact