[scudo] Use TestAllocator wrapper to ensure proper cleanup (#160800) Instead of directly instantiating scudo::Allocator, using the test TestAllocator wrapper class ensures that unmapTestOnly is called at the end of the test. This fixes the issue of QuarantineIterateOverChunks failing on Fuchsia because of a clobbered TLS pointer left by QuarantineEnabled. GitOrigin-RevId: d0a260b1d124dcad62102011aa80df5f868d28f7