Scrolling and expanding folders in sidebar is slow

### Expected Behavior

Scrolling in the sidebar should be smooth and expanding folders should be instant.

### Actual Behavior

Scrolling in the sidebar is laggy and expanding a folder takes more than a second regardless of how many requests it contains.

### Reproduction Steps

_No response_

### Is there an existing issue for this?

- [x] I have searched the [issue tracker](https://www.github.com/Kong/insomnia/issues) for this problem.

### Which sync method do you use?

- [ ] Git sync.
- [ ] Insomnia Cloud sync.
- [ ] Local only

### Additional Information

_No response_

### Insomnia Version

11.2.0

### What operating system are you using?

Windows

### Operating System Version

Windows_NT x64 10.0.26100

### Installation method

Download

### Last Known Working Insomnia version

_No response_

Start by reproducing the laggy sidebar scrolling and delayed folder expansion in Insomnia 11.2.0 on Windows, using a workspace with requests in folders. Profile the sidebar while scrolling and expanding folders, then verify that scrolling is smooth and expansion is effectively immediate without regressing normal sidebar behavior.

Written by the indexing model from the issue text.