Fixed duplicate loading of .obj model causing material ID errors

[erikwski]

I'm excited to make my first contribution to the project!

This pull request addresses the issue described in the closed issue: #1403, where loading an .obj model could result in the creation of unnecessary "Default" materials or duplicate materials.

I've implemented a solution based on approaches used in my previous projects, which effectively prevents these issues.

Key changes:

• Don't create a Default material everytime that parse a MTL file
• The Material id is generated using the node id + "_" + material.id
• If the material of the same type of node try to be created again, just link the instance to the new component setted in _ownedComponents attributes

Testing:

I've thoroughly tested this solution in my local environment to ensure it resolves the issue without introducing any regressions.
I welcome any feedback or suggestions you may have.

Thank you for your time!