hdp-provider crate to be stateful

[rkdud007]

Context

hdp-provider crate is responsible to get request and fetch the proofs of MPT/MMR. As we have introduced caching mechanism for fetching proofs, suggest to have this data structure implementation in provider crate, so that we can interact sn-mpt via library call during processing provider step.

This gives two benefit:

• utilize state (db) on preprocessor, to make step spilt not get limited from stateless environment like now
• we don't need unnecessary instance or IO call to make sn-mpt into seperate server deployment.