Hive-style partitioning

Encoding partition values in the object key path, so a reader infers them from the directory structure. It is simple, portable and universally understood, and it is why so much of the lake looks like a folder tree. Its weaknesses are what the table formats fix: renaming a partition scheme means rewriting every path, listing is expensive at scale, and the partition value is a string that must be parsed rather than a typed column.