Add unit tests for generateNumberToBeGuessed() and isCorrectGuess() methods

- Verified structure and value bounds of generateNumberToBeGuessed()
- Tested correct and incorrect input behavior of isCorrectGuess()
- Set up JUnit 5 with @BeforeEach for Game instantiation
- Improved test readability with @DisplayName annotations

.idea/encodings.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding">
+    <file url="file://$PROJECT_DIR$/src/main/java" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/src/main/resources" charset="UTF-8" />
+  </component>
+</project>