Virtual concatenation support for `concat_on_disk`

[selmanozleyen]

H5ad already supports this but I am not sure Kerchunk supports Zarr v3, last time I tried it didn't work. Maybe not high priority but nice to have if we get performance complains from concat_on_disk.

Already have a PR on this: #2032

[ilan-gold]

@selmanozleyen can you link to your PR maybe?