Fix toJSON mixin shadowing and implement dynamic mixin serialization

Problem: When Neo.setupClass applies mixins, it copies the toJSON method from the mixin (e.g., Neo.core.Observable) onto the target class's prototype. If the target class (e.g., Neo.component.Abstract) relies on inheritance for toJSON or implements its own, the mixin's version overwrites it. This results in missing data (e.g., component-specific fields) in the serialized output.

Challenge: The proposed fix is to have Neo.core.Base.prototype.toJSON dynamically invoke toJSON on all applied mixins to aggregate their data. However, many mixins (like Observable) extend Base and call super.toJSON() in their implementation. If Base.toJSON calls mixin.toJSON.call(this), and that mixin calls super.toJSON() (which resolves to Base.toJSON), it triggers infinite recursion.

Solution:

1. Prevent Shadowing: Update src/Neo.mjs to add 'toJSON' to the ignoreMixin list. This ensures the class's own toJSON (or its inherited chain) is preserved.
2. Dynamic Aggregation with Recursion Guard: Update src/core/Base.mjs:
   • Add a recursion guard (e.g., this.__inToJSON) to toJSON.
   • If the method is re-entered (via a mixin calling super), return only the base instance data to break the loop.
   • If it's the primary call, calculate base data, then recursively flatten this.mixins and invoke toJSON on each, merging the results.