fix: migrate synctest.Run to synctest.Test (Go 1.25 GA API)

In Go 1.25, synctest.Run was renamed to synctest.Test(t, func(t *testing.T)).
The old Run function only exists behind GOEXPERIMENT=synctest as a migration
bridge and will be removed in Go 1.26.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: erraggy

internal/mcpserver/input_test.go

@@ -191,7 +191,7 @@ func TestSpecInput_ResolveCacheDisabled(t *testing.T) {
 }
 
 func TestSpecCache_TTLExpiry(t *testing.T) {
-	synctest.Run(func() {
+	synctest.Test(t, func(t *testing.T) {
 		c := &specCacheStore{
 			entries: make(map[string]*cacheEntry),
 			maxSize: 10,
@@ -224,7 +224,7 @@ func TestSpecCache_TTLNotExpired(t *testing.T) {
 }
 
 func TestSpecCache_Sweep(t *testing.T) {
-	synctest.Run(func() {
+	synctest.Test(t, func(t *testing.T) {
 		c := &specCacheStore{
 			entries: make(map[string]*cacheEntry),
 			maxSize: 10,
@@ -245,7 +245,7 @@ func TestSpecCache_Sweep(t *testing.T) {
 }
 
 func TestSpecCache_Sweeper(t *testing.T) {
-	synctest.Run(func() {
+	synctest.Test(t, func(t *testing.T) {
 		c := &specCacheStore{
 			entries: make(map[string]*cacheEntry),
 			maxSize: 10,