Clicking "Hide Sidebar" and "Show Sidebar" in the UTM.app UI sometimes hangs for a few seconds (shows the spinning beachball)

**Describe the issue**
Clicking "Hide Sidebar" and "Show Sidebar" in the UTM.app UI sometimes hangs for a few seconds (shows the spinning beachball). Probably easier to notice if you click the buttons repeatedly.

Steps to reproduce:
0. Have lots of different kinds of VM's in the list on the left
1. Pick one of the VM's
2. Repeatedly click "Hide Sidebar", "Show Hidebar", "Hide Sidebar", "Show Hidebar" etc. etc. at least 10 times or so
3. Go back to 1 (pick another VM) and repeat until you see weirdness / stuttering / hangs

What happens: the animation noticeably slows down sometimes, for several seconds, shows the "macOS spinning beachball"
What I expected: no slowdowns
(also expected to see no UI animation because I have "Reduce Motion" enabled in macOS system settings, but that's another issue)

Seems to happen more on some VM's, less on others:
- macOS 13 Ventura aarch64 VM: animation does stutter, but less than the others I think
- Debian 12 (x64, QEMU): stutters a lot
- Arch Linux ARM (QEMU 7.2 ARM Virtual Machine): stutters a lot
- Fedora Linux aarch64 (uses Apple Virtualization): stutters a lot

**Configuration**
* UTM Version: Version 4.3.5 (87)
* macOS Version: 14.0 Beta (23A5328b)
* Mac Chip (Intel, M1, ...): M1 MacBook Air (16 GB RAM)

Start by reproducing the issue in the UTM.app UI with many different VM types, repeatedly toggling Hide Sidebar and Show Sidebar while switching VMs. Compare the stuttering and beachball behavior across the listed macOS, Debian, Arch Linux, and Fedora configurations; done means the sidebar transitions no longer hang or noticeably slow down.

Written by the indexing model from the issue text.