Experiment with `Core.Memory` address space

Julia 1.11 introduced `Core.Memory` and made `Array` a purely Julia type, which is nice for different optimization reasons. The interesting part for us is that `GenericMemory` has a parameter for `kind` and another for `addrspace`, which could potentially be exploited by us to store the memory managed by XLA.
This means that `ConcreteRArray`s could be managed by a simple `Array` instead, with the address space managed by Reactant.

Docs say the following:

> `addrspace` can currently only be set to Core.CPU. It is designed to permit extension by other systems such as GPUs, which might define values such as:
> ```
> module CUDA
> const Generic = bitcast(Core.AddrSpace{CUDA}, 0)
> const Global = bitcast(Core.AddrSpace{CUDA}, 1)
> end
> ```
> The exact semantics of these other addrspaces is defined by the specific backend, but will error if the user is attempting to access these on the CPU.

A lot of info is missing on how to customize this behavior but we should keep an eye on it.