Address warning diagnostics (#1395)

This addressess various warning diagnostics throughout the codebase.

docs/modules/java-binding/examples/JavaConfigExample.java

@@ -4,7 +4,7 @@ import org.pkl.config.java.JavaType;
 import org.pkl.core.ModuleSource;
 import org.junit.jupiter.api.Test;
 
-@SuppressWarnings("unused")
+@SuppressWarnings({"unused", "NewClassNamingConvention"})
 // the pkl-jvm-examples repo has a similar example
 public class JavaConfigExample {
   @Test