replace json with tls_codec serialization

[tuddman]

Summary

This patch is in DRAFT status until tls_codec serde (sans serde_json) works for our needs.

Approach

Right now sql_key_store.rs , like memorary_storage/lib.rs, rely heavily on using serde_json::to_vec and serde_json::from_slice et al, to de/serialize data into/out of the format that is needed for local storage and retrieval. Mostly the Key and Entity are conversions from/to Vec<u8> which should make this fairly straightforward.

The aim here is to modify or replace what we need to (without expanding scope) locally in this repo and/or in our fork of openmls in order to have a usable storage interface that uses the tls_codec but does not rely on serde_json nor its conversion to a json Value.

read TODOs in code comments for more thoughts.

Need to implement the serialization for the following public types

• [x] TreeSync
• [ ] openmls::prelude_test::hash_ref::HashReference
• [x] QueuedProposal
  • [x] GroupContext
  • [x] InterimTranscriptHash
  • [x] ConfirmationTag
  • [x] SignatureKeyPair
  • [x] KeyPackage
  • [x] HpkeKeyPair
  • [x] GroupState
  • [x] MessageSecrets
  • [x] ResumptionPskStore
  • [x] LeafNodeIndex
  • [x] GroupEpochSecrets
  • [x] MlsGroupJoinConfig

---

Other approach

Finish implementing any and all of the remaining serializers (and deserializers?) (spike needed - determine what's left) in https://github.com/RustCrypto/formats/tree/master/tls_codec following the pattern laid out in e.g. https://github.com/openmls/openmls/blob/12c73315a257f8377b6b7bbe8cdb694808b6e1c2/openmls/src/group/mls_group/ser.rs

[neekolas]

Given that this will break any local DBs, I'd suggest we keep this PR open until we're confident the serialization work is done. Then there's just a single breaking update for us to manage instead of multiple.

[tuddman]

Closing, in favor of https://github.com/xmtp/libxmtp/pull/845 as an alternative approach.