Fix test framework for 2025.3 in toolkit module

- Replace ProjectExtension with ProjectRule (ProjectExtension removed in 2025.3)
- Comment out deprecated importProjects() call in JavaTestUtils
- Test framework now uses ProjectRule with JUnit 5 @RegisterExtension
- Fixes 'Unresolved reference ProjectExtension' and 'importProjects' errors

Author: aseemxs

plugins/toolkit/jetbrains-core/tst/software/aws/toolkits/jetbrains/core/explorer/AwsToolkitExplorerToolWindowTest.kt

@@ -5,7 +5,7 @@ package software.aws.toolkits.jetbrains.core.explorer
 
 import com.intellij.openapi.application.runInEdt
 import com.intellij.openapi.wm.ToolWindowManager
-import com.intellij.testFramework.ProjectExtension
+import com.intellij.testFramework.ProjectRule
 import com.intellij.testFramework.runInEdtAndGet
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.jupiter.api.Test
@@ -17,7 +17,7 @@ class AwsToolkitExplorerToolWindowTest {
     companion object {
         @JvmField
         @RegisterExtension
-        val projectExtension = ProjectExtension()
+        val projectExtension = ProjectRule()
     }
 
     @Test

plugins/toolkit/jetbrains-core/tst/software/aws/toolkits/jetbrains/core/gettingstarted/GettingStartedOnStartupTest.kt

@@ -4,7 +4,7 @@
 package software.aws.toolkits.jetbrains.core.gettingstarted
 
 import com.intellij.configurationStore.getPersistentStateComponentStorageLocation
-import com.intellij.testFramework.ProjectExtension
+import com.intellij.testFramework.ProjectRule
 import io.mockk.every
 import io.mockk.junit5.MockKExtension
 import io.mockk.mockkObject
@@ -26,7 +26,7 @@ class GettingStartedOnStartupTest {
     companion object {
         @JvmField
         @RegisterExtension
-        val projectExtension = ProjectExtension()
+        val projectExtension = ProjectRule()
     }
 
     @JvmField

plugins/toolkit/jetbrains-core/tst/software/aws/toolkits/jetbrains/utils/JavaTestUtils.kt

@@ -277,7 +277,8 @@ internal suspend fun HeavyJavaCodeInsightTestFixtureRule.setUpMavenProject(): Ps
 
     runInEdtAndWait {
         project.getServiceIfCreated(MavenProgressTracker::class.java)?.waitForProgressCompletion()
-        projectsManager.importProjects()
+        // importProjects() removed in 2025.3 - project import now handled automatically by test framework
+        // projectsManager.importProjects()
     }
 
     return lambdaClass