[MENFORCER-462] Execute ReactorModuleConvergence only once

Rule checks whole reactor of current build so can be executed once in session

enforcer-rules/src/main/java/org/apache/maven/enforcer/rules/ReactorModuleConvergence.java

@@ -392,6 +392,11 @@ private void addMessageIfExist(StringBuilder sb) {
         }
     }
 
+    @Override
+    public String getCacheId() {
+        return String.valueOf(toString().hashCode());
+    }
+
     @Override
     public String toString() {
         return String.format(

enforcer-rules/src/test/java/org/apache/maven/enforcer/rules/ReactorModuleConvergenceTest.java

@@ -32,6 +32,7 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
@@ -221,6 +222,11 @@ void shouldFailWithWrongDependencyInReactor() {
         // intentionally no assertTrue() cause we expect getting an exception.
     }
 
+    @Test
+    void cacheIdShouldBeSet() {
+        assertThat(rule.getCacheId()).isNotEmpty();
+    }
+
     /**
      * This small setup is equivalent to the following situation:
      *