feat(container): add chaining, single method add method for overriding, key getter and protected entries getter

lib/src/main/java/net/tomatentum/cutin/container/LoneMethodContainer.java

@@ -6,6 +6,7 @@ import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 
 import net.tomatentum.cutin.ReflectedMethod;
 import net.tomatentum.cutin.ReflectedMethodFactory;
@@ -21,15 +22,22 @@ public class LoneMethodContainer<I extends Object> implements MethodContainer<I>
     }
 
     @Override
-    public void addMethods(ReflectedMethod<I>... methods) {
-        for (ReflectedMethod<I> reflectedMethod : methods)
-            this.methodStore.put(reflectedMethod.identifier(), reflectedMethod);
+    public MethodContainer<I> addMethod(ReflectedMethod<I> method) {
+        this.methodStore.put(method.identifier(), method);
+        return this;
     }
 
     @Override
-    public void addMethods(Object containingObject, Method... methods) {
+    public MethodContainer<I> addMethods(Object containingObject, Method... methods) {
         for (Method method : methods)
-            this.addMethods(this.factory.produce(method, containingObject));
+            this.factory.produce(method, containingObject)
+                .ifPresent(this::addMethod);
+        return this;
+    }
+
+    @Override
+    public Set<I> identifiers() {
+        return methodStore.keySet();
     }
 
     @Override