Replace allocator with mimalloc

[aumetra]

We originally used mimalloc as the allocator for Kitsune and the search service via the mimalloc crate and then switched to jemalloc as kind of a band-aid fix for unsoundness inside the mimalloc crate (they return wrongly aligned pointers. Big no no.)

There is the mimalloc-rust crate though which provides bindings that are actually sound.

I personally prefer mimalloc over jemalloc since it's smaller, faster to build, and (according to their benchmarks) outperforms a lot of other allocators.

Right now we spend ~40-50sec of our total build time on building jemalloc. We can probably reduce that with mimalloc.

[erlend-sh]

Has an issue about the unsoundness been raised in mimalloc? It appears to be more regularly updated.

[aumetra]

Yes, the issue is here: purpleprotocol/mimalloc_rust#96

Didn't seem to have gotten much attention from the maintainers though. If they fix it, I guess we can still switch.
Allocators are luckily not the hardest thing to switch in Rust.

[aumetra]

I'm just doing some little PRs on the mimalloc-rust crate right now. Their code seems largely fine, just a few small things here and there.

And I'm looking into just upgrading it to v2.x since version 2 brings improvements in memory usage and fragmentation (according to the mimalloc README)

[aumetra]

I just read through the issue again, apparently it's just an issue with the mimalloc crate when compiled with the secure feature?
That sounds a bit weird. I didn't think page protections, layout randomizations, etc. could cause unaligned pointers..

Edit: Yeah, it's probably not the secure mode (see purpleprotocol/mimalloc_rust#98)