Decentralization Client: Implement Preferred Node algorithm

[mkysel]

Is your feature request related to a problem?

In theory, the client can submit a message to any node, but the system behaves nicer if all clients select the same node for each group.

We might want to let the payer decide who to route through (xmtp/xmtpd#431) which might make this issue obsolete.

We are thinking of using stable/consistent hashing to pick a node based on the group hash and the available node pool size.

We might need a selection algorithm implemented in this library regardless of 431, if we have a payer-lite implementation in Rust that is used by self-paying bots that do not need a payer service.

Describe the solution to the problem

No response

Describe the uses cases for the feature

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Additional details

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