Clarify plugin constraints policy and normalize line endings

[IB-Tool]

### Summary
- Updated documentation to better clarify the language split policy for IB-Tool 3 plugins.
- Added a `.gitattributes` file to ensure consistent line endings and proper binary/text file handling across versions.

### Checklist
- [ ] Tests added for new features
- [ ] Code is documented
- [ ] Any dependent changes have been merged and published in downstream modules