test(skills-generator): cache remote schema across parameterized cases

RemoteSchemaValidationTest fetched and parsed the remote pml.xsd on
every parameterized invocation (199 XML files), causing redundant
network calls and flakiness risk. Load the Schema once in @BeforeAll
and reuse it, creating a fresh Validator per case.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

Author: jabrena

plinth-skills-generator/src/test/java/info/jab/pml/RemoteSchemaValidationTest.java

@@ -10,6 +10,7 @@
 import javax.xml.validation.Schema;
 import javax.xml.validation.SchemaFactory;
 import javax.xml.validation.Validator;
+import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
 
@@ -20,6 +21,17 @@ class RemoteSchemaValidationTest {
     //TODO: Use maven-central ASAP
     private static final String REMOTE_XSD = "https://jabrena.github.io/pml/schemas/0.8.0/pml.xsd";
 
+    private static Schema schema;
+
+    @BeforeAll
+    static void loadRemoteSchema() throws Exception {
+        SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
+        schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "all");
+        schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "all");
+
+        schema = schemaFactory.newSchema(URI.create(REMOTE_XSD).toURL());
+    }
+
     private static Stream<String> provideXmlFileNames() {
         return SkillReferences.xmlFilenames();
     }
@@ -33,11 +45,6 @@ void xmlFilesAreValidAgainstRemoteSchema(String fileName) throws Exception {
                 throw new IllegalStateException("Test resource not found: " + resourcePath);
             }
 
-            SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
-            schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "all");
-            schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "all");
-
-            Schema schema = schemaFactory.newSchema(URI.create(REMOTE_XSD).toURL());
             Validator validator = schema.newValidator();
 
             Source source = new StreamSource(xml);