Custom Node Process Isolation

## Background
Custom nodes often have Python dependency issues when being installed in the same environment. Our current solution is to offer a way to install custom nodes into other python environments, and be able to run different custom nodes in different python processes.

## In Scope

- Add ability to run custom nodes in separate isolated processes
- Create a virtual environment for each node pack (using `uv`)
- Goal: 50% of custom node packs (by usage) should be able to run in an isolated process for initial launch.
- ‘Repair’ that simply deletes a node environment and recreates it.