Turbopack: use mimalloc on Linux musl (#88426)
Closes #88174
With musl (i.e. Alpine), the system memory allocator can cause catastrophic slowdowns
- https://medium.com/p/stop-using-alpine-images-b51d12b0fde2
- https://nickb.dev/blog/default-musl-allocator-considered-harmful-to-performance/
We were seeing it cause a 10x slowdown, simply using mimalloc fixes this.
<img width="612" height="1091" alt="Bildschirmfoto 2026-01-12 um 15 00 29" src="https://github.com/user-attachments/assets/8de6dea3-012b-4c73-94e3-284d478bd7ef" />
<img width="1888" height="687" alt="Bildschirmfoto 2026-01-12 um 15 35 15" src="https://github.com/user-attachments/assets/d594d3ef-ae9b-468a-b022-032f1cf967e1" />
