kaish's virtual filesystem contract.
This leaf crate holds the [Filesystem] trait every VFS backend implements
and the [LocalFs] real-filesystem backend. It exists so backends that
aren't part of the kernel — most importantly GitVfs, which wraps a
LocalFs working tree — can live in their own crates without depending on
kaish-kernel.
DirEntry/DirEntryKind (the data the trait traffics in) live one layer
down in kaish-types and are re-exported here for convenience.