Sync | Rust SDK 2.0 | JSSDK 3.0

As per Fraser+Rita: _FYI - need to start adding Rust (and JS SDK, for that matter) work for 2.0.   Thinking we want to keep both clients in sync as much as possible. _There is a plan for JSSDK 3.0 - because these will be breaking changes.   Not sure of the version for the rust client……_