Performance: Importing large PMX files is extremely slow

[rintrint]

Importing large PMX files takes an unusually long time.

Steps to Reproduce:

1. Drag and drop a large PMX file into UE5 (e.g., 10–20 MB).
2. Wait for a long time until the VRM4U import options dialog appears.
3. Click "Import".
4. Wait again for a long time until the import process is complete.

I hope this can be improved in future updates. Thank you!