[refactor] reorganize devtools test nodes into modules (#6020)

## Summary

Refactored monolithic devtools node definitions into organized module
structure for better maintainability and separation of concerns.

## Changes

- **What**: Split 700+ line `dev_nodes.py` into modular structure under
`tools/devtools/nodes/` with categorized files: `errors.py`,
`inputs.py`, `models.py`, `remote.py`
- **Dependencies**: None

## Review Focus

Module import structure and ensure all node registrations are properly
preserved in the consolidated mappings.

**Before:**
```
tools/devtools/
├── __init__.py
└── dev_nodes.py (738 lines)
```

**After:**
```
tools/devtools/
├── __init__.py
├── dev_nodes.py (65 lines - imports only)
└── nodes/
    ├── __init__.py (consolidated mappings)
    ├── errors.py (error/debug nodes)
    ├── inputs.py (input/widget nodes)
    ├── models.py (model/patch nodes)
    └── remote.py (remote/combo nodes)
```

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6020-refactor-reorganize-devtools-test-nodes-into-modules-2896d73d365081e89efef7e88ca8fee3)
by [Unito](https://www.unito.io)

tools/devtools/__init__.py

@@ -97,4 +97,4 @@ async def set_settings(request: Request):
         return web.Response(status=500, text=f"Error: {str(e)}")
 
 
-__all__ = ["NODE_CLASS_MAPPINGS", "NODE_DISPLAY_NAME_MAPPINGS"]
+__all__ = ["NODE_CLASS_MAPPINGS", "NODE_DISPLAY_NAME_MAPPINGS"]