Reroutes visual and UX improvements

### What problem are you experiencing?

Reroutes align to grid based on their center by default, which makes it impossible to align them properly with the input and output sockets. A few months ago, webfiltered suggested giving them a bounding box so their position can be calculated based on that.

Since the splines render with a sort of 'average' direction, it's impossible to handle the visual noise they create unless the spline offset is set to 0, which leads to a different kind of noise. The old reroutes used a horizontal spline constrain that I think is way more useful and visually pleasing. Maybe we could have a toggle to change this behavior.

3. I also suggested in the Discord channel a while back that the splines should rescale themselves based on connection distance, just like Blender does. Here's an example.

https://github.com/user-attachments/assets/18210fcb-15b7-4476-8a25-f4862efe3186

### When does this problem occur?

Everytime I use new reroutes.

### How often do you encounter this problem?

Multiple times per day

### How much does this problem affect your workflow?

Causes moderate inconvenience

### Current workarounds

_No response_

### Ideas for solutions (Optional)

_No response_

### Additional context

_No response_

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-8838-Reroutes-visual-and-UX-improvements-3056d73d36508110aef4d6e93012c71d) by [Unito](https://www.unito.io)