Use jemalloc on ARM

As described in the 0.19.20 Release Notes jemalloc significantly reduces memory usage.

Looking through discussions in the jemalloc repo, it was recently fixed to work correctly on all ARM devices with different page sizes. See https://github.com/jemalloc/jemalloc/issues/2639, https://github.com/jemalloc/jemalloc/pull/2845#issuecomment-4276706430, https://github.com/jemalloc/jemalloc/pull/2864.

However this change was not released in the Rust library for jemalloc yet, which was last updated two years ago. So we either need to wait for an update, or find an updated fork, or specify the page size via environment variable.