vfs: handle _auditpath in proxyvfs Just forward the call to the underlying vfs.

vfs: fix proxyvfs inheritance The proxyvfs class is designed to overwrite some of the vfs logic. Yet, it did not use normal class inheritance. This is becoming an issue as `abstractvfs` method could take precedence over their `proxyvfs` version. We fix the inheritance chain to be as expected.

vfs: also audit rename Renaming through the vfs is not used in many places, and none of them seems to be a security risk. However, it is still worthwhile to run the auditing on rename file to perform developer-warning level checks.

vfs: add a `_auditpath` to abstract vfs We are about to make `rename` audit path. Since rename lives in the `abstractvfs` layer, we need it to be aware of auditing to some extent. The default implementation is no-op because multiple existing vfs are not using auditing at all right now (eg: fncachevfs).