Trusted light clients system

[tomaka]

In order to solve paritytech/substrate-connect#882, I think we should add a "trusted light client" system.

In details:

• When a connection is opened, the connection_opened callback gets an additional parameter "trusted: bool". "Trusted" means "we assume that the node isn't going to eclipse attack us". This should only ever be done for /memory nodes, but in principle it can be done for anything.
• When smoldot wants to send a request, it prioritizes full nodes. But if it's not connected to any full node, it will then send the request to a trusted light client.
• Smoldot only answers blocks and storage requests from trusted nodes.

This makes it possible to have a local peer-to-peer network of light clients that all share a single connection to a full node. The light clients that don't have the full node connection instead send requests to their trusted light client peers.

[tomaka]

Note that this is not a full solution. There's the problem of being able to track who you've made a request against in order to ban them and/or be sure the further requests aren't made towards the same target.

[tomaka]

Note that this is not a full solution. There's the problem of being able to track who you've made a request against in order to ban them and/or be sure the further requests aren't made towards the same target.

This is kind of a blocker. There's no real point in doing the above without finding a solution to this first.