[parity-util-mem] Consider using `tikv-jemallocator` instead of `jemallocator`

[ordian]

rust-lang/rust#83152
https://docs.rs/tikv-jemallocator
rust-rocksdb/rust-rocksdb#554

[koute]

Good idea; I'll try to run some basic performance/memory tests and push a PR.

[koute]

From very rough tests it looks like the CPU usage is mostly unchanged, but the peak RSS memory usage is around ~10% lower, so should be worth migrating to!