fix: private annotation codegen to include near_sdk prefix

[austinabell]

noticed doing ref-finance/ref-contracts#34 that this dep reference is incomplete and requires a user to import near_sdk::env when any function is private.

[ChaoticTempest]

Macros are fun

[mikedotexe]

Interesting, this doesn't change anything from the perspective of a contract developer, does it?

[austinabell]

Interesting, this doesn't change anything from the perspective of a contract developer, does it?

Not at all, just means they won't be required to import env if they aren't already using env (see https://github.com/near/core-contracts/blob/54f8267436058567b66efdaba3e790394f7f1529/w-near/src/lib.rs#L19 for one example of this)