indexedfs: implement Rename for directories

[Parzival-3141]

wanix/internal/indexedfs/indexedfs.go

Line 291 in 2868431

// TODO: handle case where oldname and newname are directories.

With current behavior, renaming a directory only moves the root directory file and not it's children.

[progrium]

We might want to change the schema from just a path to a name and a parent ID. This would make move/rename operations not need to change children. The tradeoff would be path lookups would be slower, but we can always cache them in memory. As long as we are careful to expire all the child paths on a move...