Restructure generated folder of codegen per version

During codegen, we should create top-level folders `v222`, ..., `v251` in `CODEGEN_OUTDIR`, so that the older versions can be conveniently deleted while packaging with Fluent.

Suggestion structure:
```
└── generated
└──
├── tui
│ ├── meshing.py
│ └── solver.py
├── datamodel
│ └── .py
├── settings
│ └── *py
├── search
│ └── *json
└── settings.zip (when zip is generated instead of the settings directory)
```