[pallas:mosaic] Added `CoreMemorySpace`
This is a specialization of a `pltpu.MemorySpace` for a specific core type.
For example, `pltpu.SMEM @ pltpu.CoreType.TC`. Not all memory space/core
type combinations are valid.
The lowering does not currently support `CoreMemorySpace`. This will be
done in a follow up.
PiperOrigin-RevId: 886153324