platformvm/config: preserve nanosecond Duration wire format for v2

v1 encoding/json marshaled time.Duration as an integer count of
nanoseconds by default; v2 has no default Duration representation and
returns a SemanticError unless told otherwise. The PlatformVM
configuration (Network, ExecutionConfig) has been on-disk-stable as
integer nanoseconds since launch — keep that wire format by passing
jsonv1.FormatDurationAsNano(true) at the Marshal/Unmarshal call sites
in GetConfig, GetExecutionConfig, and the corresponding tests that
prepare fixtures via json.Marshal.

vms/platformvm/config/config.go

@@ -5,6 +5,7 @@ package config
 
 import (
 	"github.com/go-json-experiment/json"
+	jsonv1 "github.com/go-json-experiment/json/v1"
 	"time"
 
 	"github.com/luxfi/constants"
@@ -78,5 +79,5 @@ func GetConfig(b []byte) (*Config, error) {
 		return &ec, nil
 	}
 
-	return &ec, json.Unmarshal(b, &ec)
+	return &ec, json.Unmarshal(b, &ec, jsonv1.FormatDurationAsNano(true))
 }

vms/platformvm/config/config_test.go

@@ -5,6 +5,7 @@ package config
 
 import (
 	"github.com/go-json-experiment/json"
+	jsonv1 "github.com/go-json-experiment/json/v1"
 	"reflect"
 	"testing"
 	"time"
@@ -119,7 +120,7 @@ func TestConfigUnmarshal(t *testing.T) {
 		verifyInitializedStruct(t, *expected)
 		verifyInitializedStruct(t, expected.Network)
 
-		b, err := json.Marshal(expected)
+		b, err := json.Marshal(expected, jsonv1.FormatDurationAsNano(true))
 		require.NoError(err)
 
 		actual, err := GetConfig(b)

vms/platformvm/config/execution_config.go

@@ -5,6 +5,7 @@ package config
 
 import (
 	"github.com/go-json-experiment/json"
+	jsonv1 "github.com/go-json-experiment/json/v1"
 	"time"
 
 	"github.com/luxfi/constants"
@@ -50,5 +51,5 @@ func GetExecutionConfig(b []byte) (*ExecutionConfig, error) {
 		return &ec, nil
 	}
 
-	return &ec, json.Unmarshal(b, &ec)
+	return &ec, json.Unmarshal(b, &ec, jsonv1.FormatDurationAsNano(true))
 }

vms/platformvm/config/execution_config_test.go

@@ -5,6 +5,7 @@ package config
 
 import (
 	"github.com/go-json-experiment/json"
+	jsonv1 "github.com/go-json-experiment/json/v1"
 	"testing"
 	"time"
 
@@ -77,7 +78,7 @@ func TestExecutionConfigUnmarshal(t *testing.T) {
 		verifyInitializedStruct(t, *expected)
 		verifyInitializedStruct(t, expected.Network)
 
-		b, err := json.Marshal(expected)
+		b, err := json.Marshal(expected, jsonv1.FormatDurationAsNano(true))
 		require.NoError(err)
 
 		actual, err := GetExecutionConfig(b)