Editor: Graph system serialization is broken

## Description

Graph system serialization is broken

## Steps to Reproduce

1. Run Material Editor
2. Create a few nodes
3. Save material
4. Check it in the text editor

### Expected behavior:

4. All nodes were saved

### Actual behavior:

4. No any node was saved

### Reproducibility:

100%

## Versions

2025.4

## Additional Information

n/a