[sui][refactor] Prevent developers from reading version

[666lcz]

Per comments in #493, We could consider rearranging the API's to prevent Move programmers from reading the version altogether... it's not used by any application code right now, and writing code that reads the version is bound to be hard for tools like the Move prover to reason about because the logic for updating it lives in the adapter. In addition, the new testing code doesn't mock versions (and it would be tricky to change it to do so), so this change would also prevent folks from writing tests that won't work.