xvm: preserve nanosecond Duration wire format for v2

xvm.Config embeds network.Config which has time.Duration fields. v1
encoded these as integer nanoseconds; v2 has no default representation.
Pass jsonv1.FormatDurationAsNano(true) at ParseConfig and at the test
marshal sites so the wire format is preserved.

vms/xvm/config.go

@@ -5,6 +5,7 @@ package xvm
 
 import (
 	"github.com/go-json-experiment/json"
+	jsonv1 "github.com/go-json-experiment/json/v1"
 
 	"github.com/luxfi/node/vms/xvm/config"
 	"github.com/luxfi/node/vms/xvm/network"
@@ -31,6 +32,6 @@ func ParseConfig(configBytes []byte) (Config, error) {
 	}
 
 	cfg := DefaultConfig
-	err := json.Unmarshal(configBytes, &cfg)
+	err := json.Unmarshal(configBytes, &cfg, jsonv1.FormatDurationAsNano(true))
 	return cfg, err
 }

vms/xvm/vm_security_profile_test.go

@@ -6,6 +6,7 @@ package xvm
 import (
 	"context"
 	"github.com/go-json-experiment/json"
+	jsonv1 "github.com/go-json-experiment/json/v1"
 	"errors"
 	"sync"
 	"testing"
@@ -73,7 +74,7 @@ func TestXVMInitialize_WiresSecurityProfileIntoMempool(t *testing.T) {
 		&vm.Fx{ID: propertyfx.ID, Fx: &propertyfx.Fx{}},
 	}
 
-	configBytes, err := json.Marshal(DefaultConfig)
+	configBytes, err := json.Marshal(DefaultConfig, jsonv1.FormatDurationAsNano(true))
 	require.NoError(err)
 
 	require.NoError(vmImpl.Initialize(

vms/xvm/vm_test_helpers_test.go

@@ -6,6 +6,7 @@ package xvm
 import (
 	"context"
 	"github.com/go-json-experiment/json"
+	jsonv1 "github.com/go-json-experiment/json/v1"
 	"sync"
 	"testing"
 
@@ -269,7 +270,7 @@ func setup(t testing.TB, config *envConfig) *testEnv {
 	if config.indexTransactions {
 		vmConfig.IndexTransactions = true
 	}
-	configBytes, err := json.Marshal(vmConfig)
+	configBytes, err := json.Marshal(vmConfig, jsonv1.FormatDurationAsNano(true))
 	require.NoError(err)
 
 	toEngine := make(chan vm.Message, 1)