Add supportsMultipart() hook to skip multipart test on Jetty 9.0.x

Spock AST-transforms feature methods, so @OverRide on a feature method
override triggers a compile error. Use a boolean hook instead:
- AppSecInactiveHttpServerTest.supportsMultipart() returns true by default
  and is guarded with assumeTrue() at the setup: block level
- Jetty9InactiveAppSecTest overrides to false in both jetty-server-9.0 and
  jetty-server-9.0.4, where jetty-appsec-8.1.3 range [8.1.3, 9.2.0.RC0)
  causes ParameterCollector.put(String, String) to fail → HTTP 500.

Verified locally: tests=8, skipped=3 (multipart correctly skipped), failures=0.

Author: jandro996

dd-java-agent/appsec/appsec-test-fixtures/src/main/groovy/com/datadog/appsec/AppSecInactiveHttpServerTest.groovy

@@ -139,8 +139,13 @@ abstract class AppSecInactiveHttpServerTest extends WithHttpServer {
     }
   }
 
+  protected boolean supportsMultipart() {
+    true
+  }
+
   void multipart() {
     setup:
+    assumeTrue supportsMultipart()
     def body = new MultipartBody.Builder()
       .setType(MultipartBody.FORM)
       .addFormDataPart('a', 'x')

dd-java-agent/instrumentation/jetty/jetty-server/jetty-server-9.0.4/src/test/groovy/datadog/trace/instrumentation/jetty9/Jetty9InactiveAppSecTest.groovy

@@ -2,7 +2,6 @@ package datadog.trace.instrumentation.jetty9
 
 import com.datadog.appsec.AppSecInactiveHttpServerTest
 import datadog.trace.agent.test.base.HttpServer
-import spock.lang.Ignore
 import test.JettyServer
 import test.TestHandler
 
@@ -14,10 +13,8 @@ class Jetty9InactiveAppSecTest extends AppSecInactiveHttpServerTest {
   // jetty-appsec-8.1.3 covers [8.1.3, 9.2.0.RC0) which includes Jetty 9.0.x.
   // It instruments extractContentParameters() but calls ParameterCollector.put(String, String)
   // which does not exist in Jetty 9.0.x → HTTP 500 on multipart requests.
-  @Ignore('multipart not supported on Jetty 9.0.x due to jetty-appsec-8.1.3 range conflict')
   @Override
-  void multipart() {
-    setup:
-    true
+  protected boolean supportsMultipart() {
+    false
   }
 }

dd-java-agent/instrumentation/jetty/jetty-server/jetty-server-9.0/src/test/groovy/datadog/trace/instrumentation/jetty9/Jetty9InactiveAppSecTest.groovy

@@ -2,7 +2,6 @@ package datadog.trace.instrumentation.jetty9
 
 import com.datadog.appsec.AppSecInactiveHttpServerTest
 import datadog.trace.agent.test.base.HttpServer
-import spock.lang.Ignore
 import test.JettyServer
 import test.TestHandler
 
@@ -14,10 +13,8 @@ class Jetty9InactiveAppSecTest extends AppSecInactiveHttpServerTest {
   // jetty-appsec-8.1.3 covers [8.1.3, 9.2.0.RC0) which includes Jetty 9.0.x.
   // It instruments extractContentParameters() but calls ParameterCollector.put(String, String)
   // which does not exist in Jetty 9.0.x → HTTP 500 on multipart requests.
-  @Ignore('multipart not supported on Jetty 9.0.x due to jetty-appsec-8.1.3 range conflict')
   @Override
-  void multipart() {
-    setup:
-    true
+  protected boolean supportsMultipart() {
+    false
   }
 }