## Why this should be merged
Provides access to extra payloads registered on `types.SlimAccount`, not
just on regular `types.StateAccount`. This is a breaking syntax change
to have the method reflect the behaviour.
## How this works
Modify existing method to accept the `ExtraPayloadCarrier` interface
instead of `*StateAccount`. The interface is implemented by both
`*StateAccount` and `*SlimAccount`.
## How this was tested
Covered by existing testing.
## Why this should be merged
Fixes invariant broken by introduction of `types.StateAccountExtra`.
## How this works
`state.stateObject.empty()` now also requires that the underlying
account's `Extra` field carries the zero value if a type is registered,
or is itself nil.
## How this was tested
New unit test.
---------
Co-authored-by: Darioush Jalali <darioush.jalali@avalabs.org>
