Migrating existing resources to Pandora breaks Godot

[bitbrain]

Godot version: 4.0.1
Pandora version: 1.0alpha1

Describe the bug

When trying to migrate a game over to Pandora, one would usually go and change the extends Resource to extends PandoraEntity. However, any existing .tres file that is based on said resource fails to load and it produces a set of errors in Godot. This due to the fact that .tres files are initialised with a default constructor _init() while Pandora resources come with a custom constructor (which breaks things).

To solve this, the _init() on entities could be moved into a lazy init function, but makes it more risky to work with, as a PandoraEntity may be forgotten to be initialised correctly.