Make Ubuntu packages 90% faster by rebuilding them

🔗Make Ubuntu packages 90% faster by rebuilding them

1. Rebuilding just the package itself results in small improvements
2. Rebuild with clang and better flags
3. Rebuild with mimalloc, an allocator from microsoft. “me-malloc” is a general purpose allocator with excellent performance characteristics. Initially developed by Daan Leijen for the runtime systems of the Koka and Lean languages.