transformed JenaRosenkeller importer to use Result-driven pipeline

Signed-off-by: Stephan Richter <s.richter@srsoftware.de>

de.srsoftware.cal.api/build.gradle.kts

@@ -1,4 +1,5 @@
 description = "OpenCloudCal : API"
 
 dependencies {
+    implementation("de.srsoftware:tools.util:1.1.1")
 }

de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Appointment.java

@@ -60,6 +60,13 @@ public interface Appointment {
 	 */
 	Set<String> tags();
 
+
+	/**
+	 * the title of the appointment
+	 * @return the title
+	 */
+	String title();
+
 	/**
 	 * set of Links that point to related information
 	 * @return set of links

de.srsoftware.cal.api/src/main/java/de/srsoftware/cal/api/Importer.java

@@ -1,8 +1,9 @@
 /* © SRSoftware 2024 */
 package de.srsoftware.cal.api;
 
+import de.srsoftware.tools.Result;
 import java.io.IOException;
-import java.util.List;
+import java.util.stream.Stream;
 
 /**
  * Instances of this class can be used to read Appointments from various sources
@@ -18,5 +19,5 @@ public interface Importer {
 	 * get the list of appointments from the source associated with this importer
 	 * @return a list of appointments
 	 */
-	List<Appointment> fetch() throws IOException;
+	Stream<Result<Appointment>> fetch() throws IOException;
 }