feat(fvm): wire return_codec through FFI

Ref: filecoin-project/ref-fvm#2264

Add return_codec to FvmMachineExecuteResponse and populate it from
the FVM ApplyRet. The v2/v3 engine adapters default to 0. The Go
bindings read it into the ApplyRet.ReturnCodec field.

Author: rvagg

cgo/types.go

@@ -110,6 +110,7 @@ type FvmMachineExecuteResponseGo struct {
 	FailureInfo          string
 	Events               []byte
 	EventsRoot           []byte
+	ReturnCodec          uint64
 }
 
 func (ptr SliceBoxedUint8) slice() []byte {

cgo/types_fvm.go

@@ -76,5 +76,6 @@ func (r FvmMachineExecuteResponse) copy() FvmMachineExecuteResponseGo {
 		FailureInfo:          string((*SliceBoxedUint8)(&r.failure_info).slice()),
 		Events:               (*SliceBoxedUint8)(&r.events).copy(),
 		EventsRoot:           (*SliceBoxedUint8)(&r.events_root).copy(),
+		ReturnCodec:          uint64(r.return_codec),
 	}
 }

fvm.go

@@ -178,6 +178,7 @@ func buildResponse(resp cgo.FvmMachineExecuteResponseGo) (*ApplyRet, error) {
 		FailureInfo:        resp.FailureInfo,
 		EventsRoot:         eventsRoot,
 		EventsBytes:        resp.Events,
+		ReturnCodec:        resp.ReturnCodec,
 	}, nil
 }
 
@@ -206,6 +207,7 @@ type ApplyRet struct {
 	FailureInfo        string
 	EventsRoot         *cid.Cid
 	EventsBytes        []byte
+	ReturnCodec        uint64
 }
 
 // NOTE: We only support 64bit platforms

fvm_stub.go

@@ -66,6 +66,7 @@ type ApplyRet struct {
 	FailureInfo        string
 	EventsRoot         *cid.Cid
 	EventsBytes        []byte
+	ReturnCodec        uint64
 }
 
 // Ensure cgo.Externs referenced to avoid unused import when stubbed