feat: abstract provider side to decouple store and networking protocol #180
Description
Some users remarked that the network protocol and the storage is too coupled.
On the get side, it is already possible to use the iroh-blobs protocol without a store, although of course with a bit of extra effort. But on the provider side you either need a Store, or you need to implement the entire protocol manually. Helper fns like https://docs.rs/iroh-blobs/latest/iroh_blobs/provider/fn.handle_get.html require a Store instance.
We could abstract this side as well, e.g. by having a trait or other abstraction (protocol subset?) that only handles the part of the store that is needed for handling get. The default would still be to take a Store, so default usage would not change much. Besides, even handle_connection and handle_get are already low level fns that normal users that use the protocol handler are not exposed to.