Better usage of slab allocator for vnode caching

[Kyota-exe]

As of now, vnodes contain a field nextInCache which is a pointer to the next node in a linked list of cached vnodes. Since a slab allocator is utilized in KMalloc (which is used when allocating the cached vnodes), vnode caching can be enhanced by using a custom slab allocator with a “search” method for searching a vnode in the cache.

This would allow the removal of the nextInCache pointer, saving an arguably trivial 8 bytes per vnode, but most importantly, it would abstract away the concept of “caching vnodes” from the vnode struct itself.