Fix JaCoCo coverage exclusion using proper rules configuration

Changed from simple excludes to JaCoCo rules with explicit exclude pattern.
This properly excludes Sample*Test classes from coverage requirements while
maintaining the 40% line / 30% branch coverage thresholds for the actual library code.

Author: Changjian Wang

sdk/contentunderstanding/azure-ai-contentunderstanding/pom.xml

@@ -47,8 +47,6 @@
     <jacoco.min.branchcoverage>0.30</jacoco.min.branchcoverage>
     <!-- Exclude generated sample files from Checkstyle validation -->
     <checkstyle.excludes>**/generated/Sample*Test.java,**/samples/Sample*.java</checkstyle.excludes>
-    <!-- Exclude generated sample test files from JaCoCo coverage (they are integration tests requiring credentials) -->
-    <jacoco.maven.plugin.excludes>**/generated/Sample*Test.class</jacoco.maven.plugin.excludes>
   </properties>
   <dependencies>
     <dependency>
@@ -82,9 +80,26 @@
         <artifactId>jacoco-maven-plugin</artifactId>
         <version>0.8.13</version> <!-- {x-version-update;org.jacoco:jacoco-maven-plugin;external_dependency} -->
         <configuration>
-          <excludes>
-            <exclude>${jacoco.maven.plugin.excludes}</exclude>
-          </excludes>
+          <rules>
+            <rule>
+              <element>BUNDLE</element>
+              <excludes>
+                <exclude>**/generated/Sample*Test</exclude>
+              </excludes>
+              <limits>
+                <limit>
+                  <counter>LINE</counter>
+                  <value>COVEREDRATIO</value>
+                  <minimum>0.40</minimum>
+                </limit>
+                <limit>
+                  <counter>BRANCH</counter>
+                  <value>COVEREDRATIO</value>
+                  <minimum>0.30</minimum>
+                </limit>
+              </limits>
+            </rule>
+          </rules>
         </configuration>
       </plugin>
     </plugins>