Recent (3.12+) macOS builds crash on exit.

**Describe the bug**

Since about the first rawaudio builds, i noticed the Jamulus client sometimes crashing when exiting the app. This has been reported along the rawaudio build discussions by several users though no clear link to the patch could be found, so might as well be unrelated.

Also, latest 4.0 beta1 sometimes crashes on my native M1 build, stacktrace by Apple crash reporter is not super helpful but at least dumps some lines about malloc / mutex calls.

What is interesting is, that @ann0see by accident left a Copilot code analysis report of the iOS build in which points to the same direction. Nowadays, macOS and iOS/iPadOS on Apple Silicon share a lot of framework and libs, if not even system libs and kernel (not sure). So there might be a relationship to the Copilot report.

**To Reproduce**

Very hard to reproduce. Install latest 4.0 beta1 on Apple Silicon (M1 Pro for me). Run, exit, run, exit, run, exit... sometimes after a few attempts Apple reports an app crash with dump.

**Expected behavior**

It does not crash on exit ;-)

**Screenshots**

n/a

**Operating system**

macOS 26.5.1 on Apple Silicon M1 Pro

**Version of Jamulus**

4.0.0 beta1, happens since ~3.11 git versions

**Additional context**

See discussion here:

Start with the repeated run/exit reproduction on the latest 4.0 beta1 Apple Silicon build and collect the Apple crash reporter output. Compare the malloc/mutex traces with the linked iOS Copilot analysis and the discussion at #3654; done means repeated exits no longer produce a crash and the behavior is covered by regression evidence.

Written by the indexing model from the issue text.