Use single-class imports

Author: malczuuu

src/main/java/io/github/malczuuu/problem4j/core/Problem.java

@@ -2,7 +2,13 @@
 
 import java.io.Serializable;
 import java.net.URI;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
 import java.util.stream.Collectors;
 
 /**

src/test/java/io/github/malczuuu/problem4j/core/ProblemStatusTests.java

@@ -1,6 +1,7 @@
 package io.github.malczuuu.problem4j.core;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.Optional;
 import org.junit.jupiter.params.ParameterizedTest;