Redefines the identifier API of the kind of a `PjRtMemorySpace`:
Redefines the identifier API of the kind of a `PjRtMemorySpace`:
1) `PjRtMemorySpace::kind()` returns a verbose string identifying the kind of a `PjRtMemorySpace` instance. For instance, "device", "pinned_host".
2) `PjRtMemorySpace::kind_id()` returns a unique ID identifying the kind ID of a `PjRtMemorySpace` instance. This is useful for quickly comparing the kinds of memory spaces.
