[REFACTOR] minor update to RemoteMixtureOfExperts interface

[justheuristic]

[This is a low priority issue, we can solve it alongside something else]

The hivemind-server (cli) currently defines expert names in the form of expert_pattern (e.g. ffn.[0:256].[0:256]), while RemoteMixtureOfExperts needs explicit grid sizes.

It would be great to switch to a common interface (e.g. use expert patterm in RemoteMixtureOfExperts)