feat: Enhance CustomElement with validation and customization capabilities

Summary of changes
- Added validation for options in CustomElement constructor.
- Implemented a new mechanism to set customization values using a Map.
- Updated customization getter to return a new Map.

Changes
- In the constructor, validated if the options are correctly defined. This prevents potential issues down the line if the options are not an object.
- Introducing a Pathfinder that allows for setting deep customization values using a Map. This makes it easier to manipulate specific values without redefining the entire structure, preserving the original defaults.
- Updated the customization property getter to ensure it returns a Map instead of an object, thus aligning with the new customization mechanism.

These changes improve the robustness of the CustomElement, ensuring users have more flexibility while maintaining a safety net against misconfigurations.

source/dom/customelement.mjs

@@ -197,9 +197,22 @@ class CustomElement extends HTMLElement {
 		super();
 
 		this[attributeObserverSymbol] = {};
-		this[internalSymbol] = new ProxyObserver({
-			options: initOptionsFromAttributes(this, extend({}, this.defaults)),
+
+		const options = initOptionsFromAttributes(this, extend({}, this.defaults));
+		if (!isObject(options)) {
+			throw new Error(
+				`The options are not defined correctly in the ${this.getTag()} element.`,
+			);
+		}
+
+		if (this.customization instanceof Map) {
+			const pathfinder = new Pathfinder(options);
+			this.customization.forEach((value, key) => {
+				pathfinder.setVia(key, value);
 			});
+		}
+
+		this[internalSymbol] = new ProxyObserver({ options });
 		this[initMethodSymbol]();
 		initOptionObserver.call(this);
 		this[scriptHostElementSymbol] = [];
@@ -249,6 +262,17 @@ class CustomElement extends HTMLElement {
 		return this;
 	}
 
+	/**
+	 * The `customization` property allows overwriting the defaults.
+	 * Unlike the defaults that expect an object, the customization is a Map.
+	 * This also allows overwriting individual values in a deeper structure
+	 * without having to redefine the entire structure and thus changing the defaults.
+	 * @returns {Map}
+	 */
+	get customization() {
+		return new Map();
+	}
+
 	/**
 	 * The `defaults` property defines the default values for a control. If you want to override these,
 	 * you can use various methods, which are described in the documentation available at