[Feature Request]: Preserve partially connected "dot" reroutes

### Is there an existing issue for this?

- [x] I have searched the existing issues and checked the recent builds/commits

### What would your feature do ?

When copying or deleting parts of node graph, any dot which isn't fully connected (has both input and at least one output) are removed. This makes it impossible to "prepare" dots as input/output slots to be connected later. Like, if I set up this part designed to extend down, dot won't be copied:


It would be nice to keep all the "dangling" dots during all the operations - even have dots with no outputs connected. They could be easily removed with just one keystroke.

### Proposed workflow

1. When copying parts of graph, all the dots are copied, too - even the ones at the entrance/exit part of the graph.
2. When deleting a node connected as the only dot's input/output, keep the dot.
3. When executing a graph, all the dots with no input could just throw an error.

### Additional information

_No response_

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-4306-Feature-Request-Preserve-partially-connected-dot-reroutes-2226d73d365081399478ece4d896fc24) by [Unito](https://www.unito.io)