Spec compliant HAMT keys

[ZenGround0]

The fungible token state uses ActorIDs directly as keys in the HAMTs in its state. This is not spec compliant because ActorIDs serialize as cbor ints. This is something that the HAMT library should have caught with type checking but unfortunately this is not yet the case (filecoin-project/ref-fvm#900).

For now the right way to handle this is to wrap integer serializing keys in a byte serializing type here's an example in the power actor.